
Book 




U. S. DEPARTMENT OF AGRICULTURE, 

BUREAU OF ENTOMOLOGY— BULLETIN No. 100. 

L. O. HOWARD, Entomologist and Chief of Bureau. 



THE INSECT ENEMIES OF THE 
COTTON BOLL WEEVIL. 



W. DWIGHT PIERCE, 

Agent and Expert, 

ASSISTED BY 

R. A. CUSmiAN AND C. E. HOOD, 

Agents and Experts, 

UNDER THE DIRECTION OF 

W. D. HUNTER, 

Agent and Expert, 
In Charge of Southern Field Crop Insect Investigations. 



Issued April .S, 1912. 




y 



WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1912. 



/ 



U. S. DEPARTMENT OF AGRICULTURE, 

BUREAU OF ENTOMOLOGY— BULLETIN No. 100. 

L. O. HOWARD. Entomologist and Chief of Bureau. 



THE INSECT ENEMIES OF THE 
COTTON BOLL WEEVIL. • 



W. DWIGHT PIERCE, 

Agent and Expert, 

ASSISTED BY 

R. A. CUSHIIAN AND C. E. HOOD, 



Agents and Experts, 

UNDER THE DIRECTION OF 



W. D. HUNTER, 

Agent and Expert, 
In Charge of Southern Field Crop Insect Investigations. 



Issued April 3, 1912. 




WASHINGTON: 

GOVERNMENT PRINTING OFFIOE, 

1912. 



9 (^ 



'-^'tc^ 



,CST7 



B UREA U OF ENTOMOLOGY. 

L. O. Howard, Entomologist and Chief of Bureau . 
C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. 
R. S. Clifton, Executive Assistant. 
W. F. Tastet, Chief Clerk. 

F. H. Chittenden, in charge of truck crop and stored product insect investigations. 

A. D. Hopkins, in charge of forest insect investigations. 

W. D. Hunter, in charge of southern field crop insect investigations. 

F. M. Webster, in charge of cereal and forage insect investigations. 

A. L. Quaintance, in charge of deciduous fruit insect investigations. 

E. F. Phillips, in charge of bee culture. 

D. M. Rogers, wl charge of preventing spread of moths , field tvork. 
RoLLA P. Currie, in charge of editorial work. 
Mabel Colcord, in charge of library. 

Southern Field Crop Insect Investigations. 
W. D. Hunter, in charge. 

W. D. Pierce, J. D. Mitchell, G. D. Smith, E. A. McGregor, Harry Pinkus, 
W. A. Thomas, D. C. Parman, B. R. Coad, engaged in cotton boll weevil inves- 
tigations. 

F. C. BisHOPP, A. H. Jennings, H. P. Wood, W. V. King, G. N. Wolcott, engaged 
in tick life-history investigations. 

A. C. Morgan, G. A. Runner, S. E. Crumb, engaged in tobacco insect investigations. 
J. L. Webb, T. E. Holloway, E. R. Barber, engaged in sugar cane and rice insect 

investigations. 
R. A. CooLEY, D. L. Van Dine, Wilmon Newell, A. F. Conradi, C. C. Krumbhaar, 

collaborators. 
2 

f^. m % 

^^^ ^5 191? 



LETTER OF TRANSMITTAL. 



U. S. Department of Agriculture, 

Bureau of Entomology, 
Washington, D. C, September 28, 1911. 
Sir: I have the honor to transmit herewith a manuscript entitled 
"The Insect Enemies of the Cotton Boll Weevil," by Messrs. W. 
Dwight Pierce, R. A. Cushman, and C. E. Hood, agents and experts 
engaged in cotton boll weevil investigations. The present manu- 
script contains a complete summary of the studies of the boll-weevil 
parasites conducted since 1905. The boll weevil is now known to 
be attacked by 29 species of parasites and 26 species of predatory 
insects, most of which are indigenous to the United States. It is the 
purpose of this manuscript to show the sources and value of these 
enemies and to indicate how they may be utilized to the advantage of 
the farmers of the cotton belt. I recommend the publication of this 
manuscript as Bulletin No. 100 of the Bureau of Entomology. 
Respectfully, 

L. O. Howard, 
Entomologist and CJiief of Bureau. 
Hon. James Wilson, 

Secretary of Agriculture. 



CONTENTS. 



Page. 

lutroductiou 9 

Conduct of the parasite project 10 

Historical data H 

Scope of present report 12 

Part I. The status of the cotton boll weevil and its enemies. 

1. A general chronological study of the insect control of the boll weevil. . 13 

2. Nature and sources of the material examined 14 

3. Seasonal studies of insect control, by class of infested material 14 

4. A geographic study of the statistics of insect control 20 

5. A study of the share of insect control in the mortality of immatui-e Ixill 

weevils 22 

6. A study of how agriculture modifies insect control 30 

7. Climatic considerations 32 

8. How insect control follows the dispersion of the boll wee\il 35 

9. The status of the boll weevil and its control by insects 37 

10. A brief statement of the various classes of control exercised uj^on the 

boll weevil 38 

11. Practical conclusions derived from statistical studies 38 

Part II. Biological complex. 

1. A list of the insect enemies of the cotton boll weevil 40 

2. The hosts of boll-weevil parasites 42 

3. Mites which attack the boll weevil 43 

4. Flies which parasitize the boll weevil 47 

5. The hymenopterous parasites of the boll weevil 48 

G. Biological notes upon the parasites of the weevil 54 

7. The develojament of the parasites 57 

8. The distribution of the parasites 61 

9. The parasite seasons 62 

10. Adjustment to new hosts 66 

11. Beetles which prey upon the boll weevil 68 

12. Lepidopterous larva- which are incidentally predatory upon the boll 

weevil 69 

13. Ants which prey upon the boll weevil 69 

14. Biology of the cohosts of the boll-weevil i^arasites 73 

15. A list of the host plants of the cohost weevils 80 

16. A summary of the more important biological facts 82 

Part III. The economic application. 

1. The economic principles involved 83 

2. Interpretation of parasite statistics 85 

3. Interpretation of the biological complex 86 

4. How to i^rofit by existing conditions 86 

5. How to plan for the greatest possible control -90 

6. Propagation and artificial introductions 91 

7. Objectionable practices 93 

8. The economic significance of the investigation 94 

Bibliography 97 

5 



ILLUSTRATIONS. 



PLATES. 

Page. 

Plate I. Shedding and retention of forms on the cotton plant. Fig. 1. — Normal 

scars left by shed forms. Fig. 2. — Abnormal scars with forms 

retained. Fig. 3.— Longitudinal section through base of retained 

form IG 

II. Eggs of boll-weevil parasites. Fig. 1. — Mierodontonicrus anthonomi. 

Fig. 2. — Unidentified egg. Fig. 3. — Cerambycobiiis cyaniceps. 

Fig. 4. — Eurytoma tylodermatis. Fig. 5. — Catolaccus hunter i. Fig. 

6. — Unidentified egg 56 

III. Parasites of weevils. Fig. 1. — Eurytorna tylodermatis, Tpu^pa. Fig. 2. — 

Catolaccus incertus, pupa. Fig. 3. — Cerambycobiiis cyaniceps, pupa. 

Fig. 4. — Microdontomerus anthonomi, pujaa. Fig. 5. — Larva of 

Microbracon. Fig. G. — ilicrobraconmellitor, \:)upa. Fig. 7. — Larva 

of chalcidoid 56 

TEXT FIGURES. 

Fig. 1. Diagram illustrating the monthly percentage of mortality of immature 

boll weevils due to insect enemies 19 

2. Diagram illustrating the average climatic and insect control of the 

immature boll weevils during 190G, 1907, 1908, and 1909, in hanging 
squares 21 

3. Diagram illustrating the average climatic and insect control of the 

immature boll weevils during 1906, 1907, 1908, and 1909, in fallen 
squares 22 

4. Diagram illustrating Texas climatic variations in 1907, 1908, and 1909. 36 

5. Diagram illustrating Louisiana climatic variations in 1907, 1908, and 

1909 37 

6. Diagram illustrating the boll-weevil complex 44 

7. Diagram giving the parasites of the boll weevil and their other hosts . 45 

8. Pediculoides ventricosus: Adult female, before and after inflation of 

abdomen with eggs and young 46 

9. Microdontomerus anthonomi: Adult 49 

10. Habrocytus piercei: Pupa 52 

11. Sigalphus curculionis: Male, female, antenna 53 

12. Microbracon mellitor: Adult 54 

13. Diagram illustrating yearly rank of the boll-weevil parasites, 190G, 

1907, 1908, and 1909 62 

14. Map showing the distribution of the more important parasites of the 

boll weevil 63 

15. Diagram illustrating the seasonal rotation of hosts of Catolaccus hunteri 

and Cerambycobius cyaniceps 67 

16. The "fire ant " {Solenopsis geminata): Worker 70 

17. The little black ant (J/onoHionMmmmmm/i): Adult, egg, larva, pupa . 71 

6 



INSECT ENEMIES OF THE BOLL WEEVIL. 7 

Page. 

Fig. 18. The little red ant {Monomorium pharaonis): Female and worker 72 

19. The coffee-bean weevil {Araecerusfasciculatus): Adult, larva, pupa. .. 74 

20. The blood weed weevil {Lixus scrobicoUis): Adult 75 

21. The ironweed weevil {Desmoris scapalis) : Adult 76 

22. The pepper weevil {Anthonomus eugenii): Adult 77 

23. The cowpea weevil {Chalcodermus seneus): Adult 78 

24. The plum curculio {Conotrachelus nenuphar): Larva, adult, pupa 78 

25. The potato-stalk weevil {Trichobaris trinotata): Adult, larvae, pupa3.. 79 

26. The rice weevil {Calandra oryza): Adult 80 



THE INSECT ENEMIES OP THE 
COTTON BOLL WEEVIL. 



INTRODUCTION. 

Wlaen the cotton boll weevil first entered the United States it 
appeared to have almost undisputed sway. It did, in fact, escape 
most of its enemies. But whether parasites were introduced with it 
or not, we now know that within the first three years of its existence in 
Texas it was attacked by three important species of parasites. Year 
after year new factors in its control are becoming apparent, although 
some have probably been concerned since the beginning. On the other 
hand, it is certain that entirely new elements are entering the struggle 
as rapidly as the weevil enters new biological complexes. Among the 
most striking of these new elements in the control is the recent adjust- 
ment of Microdontomerus anthonomi Crawford (fig. 9, p. 49) . This spe- 
cies was unknown until 1906 when a very few were taken in material 
reared at Cuero, Goliad, Hallettsville, Victoria, and Waco, Tex. 
In 1907 it was found to predominate in a portion of central Texas. 
In 1908 its range was found to extend northward to the Red River. 
In 1909 it was found as far east as the Mississippi River in Louisiana. 
Only a single record of the occurrence of Sigalplius curculionis Fitch 
(fig. 11, p. 53), the common parasite of the plum curculio, had been 
made prior to 1908. In that year it began to make its presence felt 
in northeastern Louisiana and western Mississippi. In 1908 a new 
chalcidoid parasite, recently described as Tetrastichus Imnteri Crawford, 
was found to be the leading parasite of the boll weevil in northern 
Louisiana and western Mssissippi. In 1909 this species was found 
as far west as Arlington, Tex. 

With the advent of each new enemy and its more complete adjust- 
ment, the power for damage possessed by the weevil is by so much 
diminished. On the other hand, every factor which checks these 
enemies without also checldng the weevil benefits the weevil. 

If the solution of the boll-weevil problem consisted merely in addmg, 
one by one, factors wliich would cut off a given percentage of the 
weevils, the time would not be distant when that might be accom- 
pHshed. The problem is far more comphcated. The various factors 
do not discriminate against one another, for wlfile lieat, ants, cold 
weather, and excessive moisture may remove many parasites from 
the struggle, it also foUows that heat, cold weather, heavy rains, 

9 



10 INSECT ENEMIES OF THE BOLL WEEVIL. 

predators, and other pests remove many ants. Proliferated plant 
tissue frequently acts as an important check upon the weevil, and yet 
in many cases it serves as a food for the weevil rather than as a con- 
trolhng force. Moist weather aids the weevil. The leaf-worm, while 
cutting off most of the weevil food, finally is checked by parasites. 
Light, heat, and dryness favor certain parasites, whereas shade and 
moisture favor others. Parasites that are normally primary fi-e- 
quently waste their energies by accidentally becoming secondary, 
and normally secondary parasites, and probably tertiary as well, also 
enter the consideration. Predatory enemies fail to distinguish the 
parasites from the weevils, but are in turn held in check by their own 
enemies. The birds devour weevils, predators, and parasites, but 
they in turn are kept down by other bu'ds and even man himself, 
and thus the complexity grows. 

There are 49 species of insects which attack the immature stages of 
the boll weevil. Of these insects 29 species may be classed as para- 
sitic, 5 as predatory larvse, and 15 as predatory adults. They are 
divided among the orders, with 3 in the Acarina, 4 in Coleoptera, 36 
in Hymenoptera, 5 in Diptera, and 1 in Lepidoptera. One of the 
acarians, 1 coleopteron, 15 Hymenoptera, and 1 dipteron, may be 
considered as quite important. A weighted average mortality of 
3.93 per cent of all immature stages may be accredited to the com- 
bined factors of all parasitic enemies; the predators are responsible 
for 15.93 per cent, while climate is responsible for 24.45 per cent, and 
plant proliferation 12.42 per cent. This makes the total natural 
control of immature stages 56.73 per cent. 

In addition to the insects attacking the boll weevils in the squares, 
there must be considered the insects which prey on the adults. These 
include one praying mantis, one predaceous bug, two beetles, and 
two ants — six species in all. 

This bulletin is not concerned with the mortality of the weevils 
after they become adult because reliable figures can not be gathered 
upon this point. It is certain that many weevils fall prey to preda- 
ceous insects and to birds, and the well-known habits of the horned 
lizard would include it in the list of possible enemies. The important 
fact is that 56 per cent of the weevil eggs fail to produce adult weevils. 
The remainder is still a formidable number but the many adverse 
influences continue to operate upon the adults and likewise upon 
their progeny. 

CONDUCT OF THE PARASITE PROJECT. 

The investigation of the insect enemies of the cotton boll weevil 
was initiated in 1 905. It has been conducted from the beginning by 
the senior author under the direction of Mr. W. D. Hunter, and with 



HISTORICAL DATA. 11 

the direct influence and encouragement of Dr. L. O. Howard, Chief 
of the Bureau of Entomology. Messrs. R. A. Cushman and C. E. 
Hood have been intimately associated in the preparation of the 
material for this bulletin since 1907. The collecting, examining, and 
recording of the immense mass of material has involved in addition 
the services of Messrs, E. A. Schwarz, J. D. Mitchell, W. E. Hinds, 
Wilmon Newell, F. C. Bishopp, A. C. Morgan, F. C. Pratt, C. R. 
Jones, W. W. Yothers, G. D. Smith, A. H. Rosenfeld, H. S. Smith, E. S. 
Tucker, T. C. Barber, S. Goes, C. S. Spooner, C. W. Flynn, T. C. Paulsen, 
J. A. Hyslop, V. I. Safro, T. E. Holloway, H. Pinkus, W. H. Hoffman, 
F. L. Elliott, and O. M. Lander. Considerable credit is due Messrs. 

E. A. Schwarz, J. C. Crawford, W. M. Wheeler, D. W. Coquillett, and 
C. H. T. Townsend for determination of the insects concerned. The 
weevils entering the biological complex have been determined by the 
senior author. In short, 33 entomologists have directly contributed 
the data which are herewith presented. 

HISTORICAL DATA. 

The first definite records of the parasites of the cotton boll weevil 
were made by C. H. T. Townsend in 1895 when he mentioned a small 
hymenopterous parasite and also recorded the suspicious occurrence 
of several species of Scymnvs in the squares, and mentioned that a 
fungoid parasite, a species of Cordyceps, "was found growing out of a 
dead pupa in its cell in a boll, November 26, in a field in San Juan 
Allende, Mexico." (Townsend, 1895.) In 1901 Profs. Herrera and 
Rangel published notes concerning the parasitic attack of Pedi- 
culoides ventricosus Newport (fig. 8, p. 46) upon the boll weevil 
(Rangel, 1901b, 1901c). 

In 1902 Dr. Wm. H. Ashmead described Bruchophagus herrerx from 
Coahuila, Mex., as a primary parasite of the boll weevil (Ashmead, 
1 902a, 1902b ; Herrera, 1 902a) . This is iprohoMy Eurn/toma tylodermatis 
Ashmead. Prof. Herrera also recorded the activities of a predaceous 
ant, Formica fusca Linn., subspecies suhpolita Mayr, variety jjerpilosa 
Wlieeler, (Herrera, 1902b; Wlieeler, 1902). In the same year Prof. 

F. W. Mally recorded the fact that Bracon (now Microhracon) mellitoi' 
Say (fig. 12, p. 54) and Eupehnus (now Cerambycohius) cyaniceps Ash- 
mead had been reared by him, since 1899, in considerable numbers 
from the boll weevil. He also recorded a species of Eurytoma. 
(Mally, 1902.) 

In 1904 Hunter and Hinds recorded additional primary parasites 
as follows: Sigalphus curculionis Fitch (fig. 11, p. 53), Catolaccus 
incertus Ashmead, Urosigalphus (rohustus Ashmead), Bracon (dorsator 
Say), and Eurytoma tylodermatis Ashmead, as well as an entomog- 
enous fungus, Aspergillus (Hunter and Hinds, 1904). The Urosi- 



12 INSECT ENEMIES OP THE BOLL. WEEVIL. 

galplius has since heen described as Vrosigalphus antlwnomi Crawford 
(Crawford, 1907a). 

In 1906 Mr. Nathan Banks described a mite, Tyroglyphus Ireviceps, 
collected at Victoria, Tex., from boll-weevil larvoe (Banks, 1906). 

In 1907 the senior author of this bulletin added Hydnocera pubescens 
LeConte as a predaceous enemy of the boll weevil (Pierce, 1907a, 1907b, 
1907c). In the same year Dr. Hinds published two papers in which 
the work of SolenojJsis geminata Fab. (fig. 16, p. 70), variety xyloni 
McCook, as a predator on the boll weevil was fully discussed, and 
considerable statistical data on the parasitic control of the weevil 
were presented (Hinds, 1907a, 1907b). Mr. Morgan published a 
brief account of the predatory attack of a bug, Apiomerus spissipes 
Say (Morgan, 1907). Mr. J. C. Crawford described as parasites of 
the boll weevil Torymus antlionomi, Urosigalphus anthonomi, and 
UrosigalpJius schwarzi (Crawford, 1907a). 

In 1 908 the senior author of this report recorded Catolaccus antho- 
nomi Ashmead as a boll- weevil parasite and Cathartus cassise Reiche 
(gemeJlatus Duval) as a predator (Pierce, 1908a, 1908b, 1908c, 1908d). 
Mr. Crawford described Ceramhycohius cushmani and Catolaccus 
Jiunteri as new parasites of the boll weevil (Crawford, 1908). During 
the same year two new predaceous enemies of the boll weevil were 
recorded from Louisiana, namely, Evartlirus sodalis LeConte and 
Evartlirus sp. (Newell and Trehearne, 1908). Mr. Townsend, in a 
paper on the muscoidean flies, recorded Ennyomma glohosa Townsend 
as a parasite of the boll weevil (Townsend, 1908). During 1909 Mr. 
Crawford described Tetrastichus liunteri as a parasite of the boll weevil 
(Crawford, 1909b). 

SCOPE OF PRESENT REPORT. 

The present report is supplementary to a former bulletin which 
was based on investigations prior to 1907 (Pierce, 1908a). The 
matter contained herein has mainly been gathered during the years 
1907, 1908, and 1909. Only such notes as are of value for the sake of 
comparison have been repeated from the previous report. 

The work is divided into three parts : 

I. The status of the cotton boll weevil and its enemies. 

II. The biological complex. 

III. The economic application. 

PART I. THE STATUS OF THE COTTON BOLL WEEVIL AND ITS 

ENEMIES. 

Part I of this bulletin shows the large mass of statistical material 
gathered during the four years of the parasite investigation, and 
attempts to place this material in such form as to show its economic 
value and significance. 



CHRONOLOGICAL STUDY OF INSECT CONTROL. 



13 



The matter is arranged topically as follows: 

1. A general chronological study of the insect control of the boll 
weevil. 

2. The nature and sources of the material examined. 

3. Seasonal studies of the insect control by class of infested material. 

4. A geograpliical study of the statistics. 

5. A study of the share of insect control in the mortality of imma- 
ture weevils. 

6. A study of how agriculture modifies insect control. 

7. Climatic considerations. 

8. How insect control follows the weevil dispersion. 

9. The status of the boll weevil and its control by insects. 

10. A brief statement of the various classes of control exercised 
upon the weevil. 

11. Practical conclusions derived from statistical studies. 

1. A GENERAL CHRONOLOGICAL STUDY OF THE INSECT CONTROL OF 

THE BOLL WEEVIL. 

Kecords upon parasitic control of the boll weevil begin in July, 
1902, and occur more or less scatteringly until June, 1906. The 
records of 1906 were very extensive, but, as will be shown, the}^ were 
merely preliminaiy . 

Table I is arranged to show the extent of the examinations made 
since 1902. This table should not be used to compare the records 
of the various years, as the manner of investigation in each year has 
been different, and the sources of the material have varied greatly. 
The table is only intended to show the total of the examinations and 
how these were distributed from year to year. A careful analysis of 
the figures has been given in the various sections of Part I. 

Table I. — Insect control of the boll weevil, by years. 



1902. 
1903. 



1905, March.. 
1905, August. 

1900 

1907 

1908 

1909 



Totals and averages . 



Weevil 

stages. 



602 

819 

1,005 

1,702 

40, 073 

13, C02 

29,349 

11,653 



98, 805 



Preda- 
tors. 



(?) 
(?) 
(?) 
(?) 

10,547 
2,279 
3,862 
1,231 



I'ara- 
sites. 



59 

32 

21 

1,728 

1,121 

2,952 

020 



6,540 



Per cent mortality due to— 



Preda- 
tors. 



(?) 
(?) 
(?) 
(?) 
26.31 
16.75 
13. 15 
10. 56 



Para- 
sites. 



1.16 
7.20 
3.18 
1.23 
4.31 
8.24 
10.05 
5.32 



1 6. 61 



All 

insects. 



(? 

(?) 

(?) 

(?) 
30. 62 
24.99 
23.20 
15.88 



1 This table should not be construed as indicating that parasite control has been falling oft, because 
the table is based upon different kinds of examinations in difierent years. The detailed analysis of these 
records will be found on subsequent pages. 



14 INSECT ENEMIES OF THE BOLL WEEVIL. 

The figures of 1902 are based on the total number of stages reared. 
The data of 1903 are based on the total number of stages reared, but 
mclude both stages in hanging and fallen forms. There were 654 
stages in fallen forms of which 14, or 2,14 per cent, were parasit- 
ized, and 165 stages in hanging forms of which 45, or 27.27 per cent, 
were parasitized. The figures of 1905 were separated to show the 
investigations of March and August because of the great difference 
in the mortality from parasites in these two months. Between 1906 
and 1909 the data represent all classes of infested material and all 
infested regions. It will be noticed that for the last four years the 
total insect control of the immature weevils has fluctuated between 

15 and 30 per cent. 

2. NATURE AND SOURCES OF THE MATERIAL EXAMINED. 

During the four years 1906-1909 examinations of mortality have 
been made of material collected at 6 places in Arkansas, 26 in Louisi- 
ana, 6 in Mississippi, 7 in Oklahoma, and 65 in Texas, making a total 
of 110 places. These examinations are based upon 94,677 stages, 
involving an individual examination of over 222,700 cotton forms 
(squares, blooms, and bolls). Many other collections and exami- 
nations were made, but because of incomplete records are excluded 
from the accompanying tables. 

During the four years there has been the equivalent of examina- 
tions in 176 localities, or an average of 44 localities per year. 

3. SEASONAL STUDIES OF INSECT CONTROL, BY CLASS OF INFESTED 

MATERIAL. 

Very shortly after the work began in 1906 it became evident that 
the activity of the parasites and other insect enemies of the weevil 
was very difi'erent in squares and bolls, and in fallen or hanging 
squares or bolls, and also that the highest control by parasites was 
in hanging squares. 

An examination of the squares of various varieties of cotton plants 
will show the observer that certain ones have a transverse attachment 
of the pedicel to the stem. In all cases where this attachment is 
perfectly transverse, the square when injured by any insect is caused 
to drop because of the separation of the infested part from the main 
stalk by the growth of an absciss layer at the point of attachment. 
(PI. I, fig. 1 ; fig. 3, a.) Certain other varieties indicate a long diag- 
onal attachment to the stem. Wlien these squares are injured, a 
diagonal absciss layer is formed which runs down the stem from one- 
half to three-fourths of an inch or even more. This layer is gen- 
erally incomplete at the lower point and consequently the square 



SEASONAL STUDIES OF INSECT CONTROL. 



15 



hangs by a few threads and dries on the plant. (PI. I, fig. 2 ; fig. 3, &.) 
To these squares and bolls which thus hang, we have applied the 
terms ''hanging squares" and "hanging bolls." 

Tables II and III, which are arranged to show the monthly per- 
centages of control by parasites, by predators, and by all insects, 
illustrate the differences in the control of the weevil in the four 
principal classes of infested material, namely, fallen and hanging dry 
squares, and fallen and hanging dry bolls. 

A few words of explanation of these tables are necessary in order 
to show what is meant by the different classes of mortality. It has 
been found that a large number of stages are destroyed as eggs or 
young larvae by the proliferation of the plant tissues. At the time 
of the examination for mortality of the weevil, all evidence of the 
weevils destroyed in these stages has disappeared; consequently the 
percentages of mortality given in the following tables are tlie per- 
centages of stages found which arc killed by the causes enumerated, 
and the mortality from proliferation is entirely ignored. 

Table II. — Monthly viortality of the boll weevil due to insects in fallen squares. 



Month. 



June 

July 

August . . . . 
September. 
October 



Totals and avora,i,'''s for 
1906 



June 

July 

August 

November. 



1907 



Totals and averages for 
1907 



May 

June 

July 

August 

September. 

October 

November. 



Totals and averases for 
1908 



January . . . 

July 

August 

September. 



Totals and averages for 
1909 



Squares 
exam- 
ined. 



4,176 

7,265 

V.),?.05 

l;),70!) 

l.ilSl 



43,736 



2,074 

5,192 

7,400 

150 



14,S16 



100 
7,808 
7,437 
1,941 
7,189 
9,678 

604 



34, 757 



50 
,677 
,507 
750 



13,984 



Stages. 
foimd. 



3,831 

4,552 

11, 186 

5,365 

600 



25,534 



1,261 

3, 60S 

5,058 

93 



10,020 



56 
5,285 
4,690 
1,208 
3,894 
5,342 
369 



20,844 



23 

4,334 

2,866 

364 



7,587 



Stages killed hy — 



Cli- 
mate. 



1,797 
1,676 
2, 8?S 
1,475 
205 



7,981 



339 

778 

2, 156 

90 



3,363 



4 

1,169 
1,{)47 
540 
578 
807 
90 



Preda- 
tors. 



914 
1,079 
4,097 
1,625 

133 



7, 848 



198 

433 

1,372 





2,003 





866 
902 
294 
815 
289 
1 



4,235 3,167 





1,318 

680 

19 





507 
428 



940 



Para- 
sites. 



lis 
207 
ISO 
285 
33 



823 



76 

133 

155 

1 



2 
324 
219 
63 
136 
659 




131 



Percentage of stages killed. 



Tofal. 



73. S 
65. 1 
63.5 
63.0 
61.8 



48.6 
37.2 
72.8 
97.7 



10.7 
44 6 
46.2 
74.2 
39.2 
32. S 
51.1 



42.7 




45. 1 
39.9 
6.8 



Preda- 
tors. 



23.8 
23.6 
36.6 
30.2 
22.1 



1.5.6 

11. 9 

27.1 





19.9 




16.4 
19.2 
243 

20.9 
5.4 
2.7 



15.2 





11.7 

14 9 

1.4 



Para- 
sites. 



.3.1 
4 7 
1.7 
5.4 
5.6 



3.3 



7.0 
3.8 
.3.0 
1.0 



3.5 
6.1 
4 7 
5.2 
3.5 
12.3 
22.6 




3.0 
1.3 
.3 



2.2 



All 

insects. 



26.9 
28.3 

38.3 
3.5.6 
27.7 



22.6 

15.7 

30.1 

1.0 



3.5 
22.5 
23. 9 
29.5 
24 4 
17.7 
25.3 




14 7 
1.5.2 
1.7 



14 6 



16 



INSECT ENEMIES OF THE BOLL WEEVIL. 



A study of Table II, on the mortality due to insects in fallen 
squares, shows that the principal insect work is that of predatory 
insects and, furthermore, that the total insect control is, as a rule, 
less than the climatic control. The table embraces the examination 
of 63,985 weevil stages of which 17,596 were killed by climate, 13,958 
by predators, and 2,849 by parasites. In other words, the average 
percentage of control in fallen squares by all kinds of insects is 26.2 
per cent, or 21,8 per cent by predators and 4,4 per cent by parasites. 

A further study of Table II shows that the predators have in each 
year done their most valuable work in the month of August. The 
parasites, however, have shown considerable variation in the month 
of their best work. In 1906 the highest average percentage was in 
October; in 1907 it was in June; in 1908 in November; and in 1909 
in July. 

Table III. — Monthly mortality of the boll weevil due to insects in hanging squares. 





Squares 
exam- 
ined. 


Stages 
found. 


Stages killed by- 


Percentage of stages killed. 


Months. 


Cli- 
mate. 


Preda- 
tors. 


Para- 
sites. 


Total. 


Preda- 
tors. 


Para- 
sites. 


All in- 
sects. 


1906 
July 


474 

4, 105 

2, 032 

33 


247 

2,566 

1,285 

20 


47 
539 
245 

4 


20 
544 
269 

10 


76 

337 

125 




57.9 
55.3 
49.7 
70.0 


8.0 
21.2 
20.9 
50.0 


21.0 

13.1 

9.7 




29.0 




34.3 




30.6 


October 


50.0 






Totals and averai:;es for 
1906 


6, 704 


4,118 


835 


843 


538 


53.8 


20.5 


13.0 


33.5 






1907 


150 

956 

3,543 


88 

513 

2,011 


26 
57 
296 


5 
16 

175 


13 
103 
580 


50.0 
34.3 
52.2 


5.7 
3.1 

8.7 


14.7 
20.1 

28.8 


20.4 


July 


23.2 




37.5 






Totals and averages for 
1907 


4,649 


2,612 


379 


196 


696 


48.6 


7.5 


26.6 


.;4.i 






190S 
July 


2,955 
1,393 
3,922 
1,192 
1,125 


2,177 
842 

2,340 

553 

10 


395 
141 
476 
116 

8 


179 
91 

259 

53 




479 
279 
410 
113 



48.4 
60.7 
48.9 
52.9 
80.0 


8.2 
10.8 
11.0 
10.0 



22.0 
33.1 
17.5 
21.2 



30.2 




43.9 


September 


28.5 


October 


31.2 











Totals and averases for 
1908 


10,587 


5,922 


1,136 


582 


1,281 


50.9 


9.8 


21.7 


31.5 






1909 


80 
630 
1,290 
745 
136 
515 


3 

383 

856 
496 
52 
169 



36 
96 

61 
14 

47 




31 

72 

21 



1 




117 
88 
76 
30 
71 




48.0 
29.9 
31.9 
100. 
70.4 




8.1 

8.4 

4.2 



6 



30.5 
10.3 
15.3 
68.0 
42.0 





July 


38.6 


August 


18.7 




19.5 




68.0 


December 


42.6 


Totals and averages for 
1909 


3,396 


1,959 


254 


125 


382 


38.8 


6.4 


19.5 


25.9 







Table III shows that the principal insect work in hanging squares 
is that of parasitic insects and, furthermore, that the total insect 
control in hanging squares is each year higher than the climatic 
control. Tliis table embraces the examination of 14,611 weevil 



I. 100, Bureau of Entomology, U. S. Dept. of Agricultu 



Plate I. 




Shedding and Retention of Forms on the Cotton Plant. 

Fi.L(. 1.— a, b, c. Normal scars left by shed forms. Fig. 2.— o, 6. '■, Atmormal .sears witli forms 
retained. Fi,?. 3.— «, Longitudinal section through base of .shed form; b. Longitudinal 
seotio7i throu.sh base of retained form. Fig. 1, natural size: fig. 2. ,v<)me\vhat reduced: 
fig. 3, enlarged two diameters. (After Hinds.) 



SEASONAL STUDIES OF INSECT CONTROL. 



17 



stages of wliich 2,604 were killed by climate, 1,746 by predators, 
and 2,897 by parasites. In other words the average percentage 
of control by all lands of insects is 31.61 per cent, or 11.93 per cent 
by predators and 19.68 per cent by parasites. It appears that July 
and August are usually the best months for parasite control in hang- 
ing squares. 

Table IV. — Monthly mortality of the boll weevil due to insects in hanging bolls. 





Bolls 

exam- 
ined. 


Stages 
found. 


Stages killed 


by- 


Percentage of stages killed. 


Months. 


Cli- 
mate. 


Preda- 
tors. 


Para- 
sites. 


Total. 


Preda- 
tors. 


Para- 
sites. 


Allm- 
sects. 


1906 


145 

2,947 

23, 454 

6,210 

399 




290 
2,977 
1,555 

147 



28 
416 
198 
21 




14 

742 

188 

11 




19 
23 
3 


0.0 
14.5 
39.5 
26.3 
23.8 


0.0 

4.8 

24.9 

12.1 

7.5 


0.0 



.0 

1.5 

2.0 


0.0 


July 


4.8 




25.5 




13.6 




9.5 






Totals and averages for 
1906 


33,155 


4,969 


603 


955 


45 


35.9 


21.9 


0.9 


22.8 






1907 


50 

60 

1,272 


5 

7 
330 


1 

1 

115 




51 


1 

4 


40.0 

14.3 
51.5 



15.4 


20. 



1.2 


20.0 


July 







16.6 






Totals and averages for 
1907 


1,372 


342 


117 


51 


5 


50.6 


14.9 


1.4 


16.3 






1908 


2,227 

4,450 

1,123 

933 


238 

405 

200 

98 


34 

125 
22 


6 

26 
20 

4 


21 

13 



1 


29.7 
40.5 
21.0 
13.2 


2.5 

6.4 
10.0 
4.1 


8.8 

3.2 



1.0 


11.3 


July 


9.6 




10.0 




5.1 






Totals and averages for 
1908 


8,733 


941 


189 


56 


35 


29.7 


5.9 


3.7 


9.6 






1909 


1,616 
716 
608 


402 
115 
56 


133 

12 
14 


25 
49 
12 


11 
2 
1 


42.0 
54.7 

48.2 


6.2 
42.6 
21.4 


2.7 
1.7 
1.7 


8.9 




44.3 


March 


23.1 






Totals and averages for 
1909 


2.940 


573 


159 


86 


14 


45.2 


15.0 


2.4 


17.4 







In fallen bolls the principal insect work is that accomplished by 
predatory insects, and the total insect control has been less than 
the climatic control except in the year 1906. Table IV covers an 
examination of 6,825 weevil stages, of which 1,128 were killed by 
climate, 1,148 by predators, and only 99 by parasites. Tliis means 
that 18.2 per cent of all the stages were killed by insects, or 16.8 
per cent by predators and 1.4 per cent by parasites. In this class 
of infested forms it is also noticeable that the principal work by 
the predators is accomplished during the month of August. 
16844°— Bull. 100—12 2 



18 INSECT ENEMIES OF THE BOLL WEEVIL. 

Table V. — Monthly mortality of the boll weevil due to insects in hanging bolls. 





Bolls 

exam- 
ined. 


Stages 
found. 


Stages killed 


by- 


Percentage of stages killed. 


Month. 


Cli- 
mate. 


Pred- 
ators. 


Para- 
sites. 


Total. 


Pred- 
ators. 


Para- 
sites. 


All 
insects. 


1900. 
July 


43-1 

S, 702 
4, 22 1 
it, 029 


22 
2,444 
1,627 
1,359 


2 

281 

i;5o 

ISO 


3 
340 

2.»2 
2i;6 



155 
111 I 
06 


22.0 
31.7 
32.1 
38.2 


13. 
13.9 
17.9 
19.0 


0.0 
6.3 
0.2 
4.8 


13.6 


.\ugust 


29.2 
24.1 


October 


24.4 






Totals and averages for 
1906 


17,049 


5,452 


599 


901 


322 


33.4 


10.5 


5.9 


22.4 






1907. 
July 


460 

683 


38 
393 


2 
35 



13 




50 


5.3 
25.0 



3.0' 



12.5 





August.. 


16.1 






Totals and averages lor 
1907 


1,143 


431 


37 


13 


50 


23.2 


3.0 


11.6 


14.6 


1908. 
February 


12.451 
1,239 
2, 132 
720 
664 
432 
519 


515 

22 
492 
191 

83 
262 
274 


424 
21 
03 
23 
7 
36 

134 





37 

7 

17 
11 

1 


54 

1 
58 
22 

5 

8 


92.8 
100.0 
32.0 
27. 2 
.31 ! 3 
19.8 
52.2 






7. 5 

3.0 

20. 4 

4.2 

.3 


10.5 
4.5 
11.7 
11.5 
2.4 
1.9 
2.9 


10.5 




4.5 


July 


19.1 


August.. 


15.1 


September 


22.8 




6.1 


November. . 


3.2 






Totals and averages for 
190S 


18,157 


1,839 


708 


73 


150 


50.6 


3.9 


8.1 


12.0 






1 909. 
January 


3,941 
430 
053 
365 

2,148 


8.57 

;« 

81 

42 

519 


335 
13 
16 

1 
217 


38 
11 
10 

13 


43 




11 


48.5 
68.6 
39.5 
8.1 
46.4 


4.4 
31.4 
19.7 

5.4 
25.0 


5.0 




2.1 


9.4 


February. . 


31.4 


March 


19.7 


August 


5.4 


December 


27.1 






Totals and averages for 
1909 


7,537 


1.5.34 


582 


SO 


54 


46. 7 


5.2 


3.5 


8.7 







SEASONAL. STUDIES OF INSECT CONTEOL. 



19 



Table V was based, as may be seen, upon the examination of 9,256 
weevil stages, of which 1,926 were killed by climate, 1,067 by pred- 
ators, and 576 by parasites. In other words, the insect enemies 
killed 17.74 per cent, of which 11.52 per cent were killed by predators 
and 6.22 per cent by parasites. July and August are the principal 
months for attack upon hanging bolls. 

Summarizing the four preceding tables, Table VI is presented to 
show the monthly rate of mortality in all classes of infested forms. 




Fig. 1.— Diagram illustrating the monthly percentage of mortality of immature boll weevils due i 

insect enemies. (Original.) 

It will be noticed that in each year certain months have been omitted 
and it must be explained that the reason therefor has been the 
necessity of making these examinations only when other work was 
not pressing. An analysis of this table is more readily made by 
reference to the accompanying diagram (fig. 1), wliich demonstrates 
conclusively that August is the month during wliich the insect enemies 
of tlie boll weevil are most active. 



20 INSECT ENEMIES OF THE BOLL WEEVIL. 

Table VI. — Monthly rate of inortalitij of the boll weevil in infested forvrs of all classes 



Month. 



1906. 

•Tune 

July 

August 

September 

October 

Totals and averages for 1906 

1907. 

June 

July 

August 

November 

Totals and averages for 1907 

1908. 

February 

March 

May 

June 

July 

August 

September 

October 

November 

Totals and averages for 1908 

1909. 

January 

February 

March 

July 

August 

September 

November 

December 

Totals and averages for 1909 



Forms 
exam- 
ined. 



4,621 
11,120 
55,686 
2.3,175 

6,042 



100, 644 



2,274 

6.658 

12, 898 

150 



21,980 



12,451 
1,329 
100 
10, 035 
16, 974 
5.177 
12,708 
11,302 
2,248 



.234 



5.087 
1,146 
1,261 
8. 307 
7,162 
1,495 
136 
2, 663 



27,857 



Stages 
found. 



3,831 
5,111 
19,173 
9,832 
2,126 



40, 073 



1,354 

4, 166 

7, 792 

93 



13,405 



515 

22 

56 

5,523 

7,764 
2,441 
6,415 
6. 157 
053 



29,546 



1,285 

150 

137 

4,717 

3, 764 

860 

52 

688 



11,653 



Percentage of stages killed by- 



All 
causes. 



73.80 
61.67 
54.64 
50.40 
44.12 



55.81 



48.67 
36.55 
64. 19 
97.70 



54.27 



92.81 
1(10. 00 
10.70 
43.81 
45.63 
61.53 
42.29 
33. 92 
50. 53 



44.34 



45.52 
58.00 
43.06 
45. .36 
37. .32 
21.25 
100. 00 
52. 32 



41.73 



Clmiate. 



46. 90 
34. 29 
21.19 
20.80 
19.56 



25.15 



27.03 
20.11 
33.39 
96.70 



29.06 



82.33 
95.50 
7.20 
15.78 
20.99 
29.79 
16. 66 
15.57 
35.52 



21.21 



36. 42 
16. 06 
21.89 
28. 70 
20.64 
9. .30 
32. 00 
38.37 



Preda- 
tors. 



23.80 
21.83 
29.32 

24.14 
19.75 



26.31 



14.99 

10.77 

20.67 





16.88 






15.78 
14.73 
16.87 
17.06 
5.73 
3.06 



13.12 



4.90 
40.00 
20.43 
11.19 
13. .33 

3.02 


2.03 



25.84 



10.56 



Para- 
sites. 



3.10 
5.53 
3.61 
5.43 
4.79 



4.31 



6.64 

5.68 

10.12 

1.00 



8.32 



10.48 
4. .50 
3. 50 
6.24 
9.90 

14.91 
8.55 

12.61 

14.70 



10.00 



4.20 
1. .33 
.72 
5!25 
3.34 
8.95 
68.00 
11.91 



5.32 



All 
insects. 



26.90 
27.36 
32.93 
29.57 
24.54 



30.62 



21.63 

16.43 

30.79 

1.00 



25.20 



10.48 
4.50 
3.50 
22.02 
24.63 
31.78 
25.61 
IS. .34 
17.76 



23.12 



9.10 
41.33 
21.15 
16.34 
16.67 
11.97 
68.00 
13.94 



15.88 



4. A GEOGRAPHIC STUDY OF THE STATISTICS OF INSECT CONTROL. 



A study of these same statistics, when arranged to show the insect 
control by States, has given much interesting Ught upon the subject 
of the control of the weevil. 

In fallen squares we find an average for total insect control of 26.8 
])er cent in Oldahoma, 25.9 per cent in Mississippi, 24.5 per cent in 
Texas, 20.6 per cent in Louisiana, and 12.5 per cent in Arkansas. 
Anal3^zing these figures from another standpoint, we find that the 
State of Mississippi leads in parasite control with 14.27 per cent, 
Oklahoma standing next with 4.71 per cent, Texas with 3.9 per cent, 
Louisiana with 2.52 per cent, and Arkansas with 0.71 per cent. The 
relative rank of the States for predatory control is quite different. 
Oklahoma leads with 22.16 per cent, Texas comes next with 20.6 per 
cent, Louisiana with 18.1 per cent, Arkansas with 11.82 per cent, 
and Mississippi with 11.63 per cent. In climatic control Texas leads 



GEOGEAPHIC STUDY OF STATISTICS. 



21 



with 37.9 per cent, Oklahoma comes next with 30. S per cent, Arkan- 
sas with 25.65 per cent, Louisiana with 12.5 per cent, and Mssissippi 
with 11.7 per cent. Thus it may be seen that the dry, prairie States 
of Texas and Oklahoma lead in the climatic and predatory control 
of the weevil and also in the total amount of control, and that the 
climatic control in each of these States is greater than the total insect 
control. Tliis latter fact is also true of Arkansas. In Louisiana 
and Mississippi, States which are naturally more humid, the chmate 
has less influence and the greater proportion of the control is by the 
insect enemies. 

In hanging squares the conditions are entirely reversed. It is 
noticeable that Oldahoma leads in parasitism with an average of 31.74 
per cent, Texas averages 2G.6 per cent, Arkansas 24.16 per cent, Mis- 
sissipi 21.2 per cent, and Louisiana 12.07 per cent. In predatory 
control Louisiana leads with 12.9 per cent, Texas comes next with 10.9 





/O 20 30 -^ SO 60 




/2.07 


12.9 




/S.69 


\ 40.66 

30 

69 


1 \ = c. 


^RASITES 
lEDATORS 
'./MATE 


LOU/S/ANA 


HBflHH 


mmm^mA 






^a^^L 




e.38 


8./ 2 


M/SSrSSIPPI 


MH^^^^r 


\36. 




— 


3/. 74 


2. S3 


26. 


ARKANSAS 


WKM- 






\S3.38 






JO. 9 


/6.8 




TEXAS 


iHUIL^ 


W////A 




\54.3 






9.53 






OKLAHOMA 


HHHHHH 


iH 


~\4/.27 















Fig. 2.— Diagram illustrating the average climatic and insect control of the immature boll weevils 
during 1906, 1907, 1908, and 1909, in hanging squares. (Original.) 

per cent, Mississippi with 6.98 per cent, and Arkansas with 2.53 per 
cent. We have no record of predatory control in Oklahoma. In all 
five States insect control in hanging squares is greater than climatic 
control. With regard to climatic control Arkansas leads with 26.69 
per cent, Texas has 16.8 per cent, Louisiana 15.89 per cent, Oldahoma 
9.53 per cent, and Mississippi 8.12 per cent. These statistics are 
graphically shown in figures 2 and 3. 

A brief comparison of the condition in hanging and fallen squares will 
show that the States of Texas and Oklahoma have a higher average 
percentage of control from all factors in fallen squares than in the 
hanging squares ; the States of Louisiana and Arkansas have a higher 
average percentage of control from all factors in hanging squares than 
in fallen squares, and in the State of ^Mississippi the difference is very 
slight, although in favor of the fallen squares. This illustrates the 



22 



INSECT ENEMIES OF THE BOLL WEEVIL. 



difficulty of giving any single recommendation for the control of the 
boll weevil whicli would apply to all regions. This i)oint wiU be 
brought out more fully in other sections of this bulletin. 

5. A STUDY OF THE SHARE OF INSECT CONTROL IN THE MORTALITY OF 
IMMATLTRE BOLL WEEVILS. 

The condensed tables which have been presented are likely to give 
the impression that the parasite control of the weevil is on an average 
very low, but it must be remembered that the examinations have 
been made in all parts of the infested region whether the weevil has 
been present 17 years or only a few months, and whether the weevil 
damage amounts to less than 1 per cent of the crop or to almost 100 



ARKANSAS 



LOU/S/A/\JA 



TEXAS, 



OKLAHOMA 



M/SS/SS/PPl\ 



PER CENT 
/a ^0^ 30 40 SO 60 


0.7> 
L II. 82 




2S.65 




8.18 

37.9 


1 \ = a.//^ArE 


im^////yf; 


^ 




\3 


2.52 

I 


18.1 


/2.S 




i^^ 


W///////A 


1 


Z333./2 


3.9 


20.6 






k^^^ 


^^//y^m^/A 


WA 








_\62.4 


4.7/ 


22./ 6 






30.8 




Z67 


[■III 


W////////A 


'f/////A 






\5 


/^.2; 


' // 


63 


//.7 


7.60 




wammtmmv//////y. 


mm 


\3 









Pig. 3. — Diagram illustrating the average climatic and insect control of the immature boll weevils 
during 1906, 1907, 1908, and 1909, in fallen squares. (Original.) 

per cent. This great difference in the sources of the inaterial exam- 
ined has necessarily lowered the average mortalitj" to its minimum. 
Tlie following records show some of the cases of very high mortality 
due to parasites: 

Highest records of parasitism of the hoU weevil. 
IN FALLEN SQUARES. 



liOealif V. 



Date. 



Number 
of stages. 



Percent- 
age of 
parasit- 
ism. 



Robson,La 

Corpus Christi, Tex 

Natchez, Miss 

Dallas, Tex 

GoUad, Tex 

Natchez, Miss 

Cuero, Tex 

Natchez, Miss 

Shreveport, La 

Victoria, Tex 

Roosevelt, Tex 

Arlington, Tex 

Brownsville, Tex. . . 

Denison, Tex 

Atoka, Okla 



Nov. 5, 1907. 
June 20, 1907. 
Oct. 23, 190S. 
Aug. 12, 190S, 
July 28, 1908. 
Oct. 16, 1908. 
Aug. 12, 1907. 
Julv, 1909... 
Oct. 29, 1908. 
June 19, 1908. 
Sept. 24, 1900 
July 17, 1908. 
Sept. 5, 1906., 
July, 1909.... 
Sept. 2, 1908.. 



53 

92 
157 

IS 
114 
230 
105 
200 
624 
513 

69 
382 
,147 
494 
100 



77.36 
36.95 
28.6 
27.78 
26.63 
21.7 
19.04 
18.5 
15.8 
14.5 
14.4 
13.35 
12.4 
8.5 
8.0 



SHAEE OF INSECT CONTROL IN WEEVIL MORTALITY, 



23 



Highest records of parasitism of the boll weevil — ("outiuued. 
IN HANGING SQUARES. 



Locality. 



Date. 



Number 
of stages. 



Percent- 
age of 
parasit- 
ism. 



Waco, Tex 

Arlington, Tex. . . 

Victoria, Tex 

Dallas, Tex 

Arlington, Tex. . . 

Dallas, Tex 

Waco, Tex 

Navasota, Tex 

Natchez, Miss 

San Antonio, Tex 
Halletts\ille, Tex 

Dallas, Tex 

Arlington, Tex. . . 

Victoria, Tex 

Foster, La 

Talliilah, La 

Forbiug, La 

Shreveport, La. .. 

Hope, Ark 

Ada, Okla 

Fouke, Ark 

Waco, Tex 

Cuero, Tex 

Tallulah.La 



July 
July 
Aug. 
Aug. 
July 
July 
July 
Aug. 
Oct. 
July 
July 
Aug. 
Aug. 
July 
Sept, 
Dec. 
Aug 
Oct. 
Sept, 
Sept, 
July 
Sept, 
Aug. 
Sept. 



23, 1909. 
,1909.... 

5, 1907.. 

17, 1907. 
17, 1908. 
,1909.... 
25, 1900. 

17, 190S. 
23,1908. 

24, 1908. 
1,1907.. 

10, 1907. 

6,1908.. 
29, 190S. 
, 7, 1907.. 
20, 1909. 

29, 1907. 

28, 1908. 
. 16, 1908 
.4, 1908.. 
27, 1908. 
. 20, 1900 
31, 1903, 
,,1909... 



26 

82 

51 

57 

99 

29 

82 

29 

19 

193 

260 

140 

22 

85 

41 

37 

69 

63 

284 

109 

347 

495 



66.6 

63.63 

61.5 

59.7 

56.86 

52. 63 

52.6 

51.75 

51.3 

48.27 

47.3 

47.15 

46.92 

45.71 

45.47 

44.7 

43.9 

37.84 

33.33 

31.74 

26.05 

23.8 

21.3 

15.35 



IN FALLEN BOLLS. 



Victoria, Tex. . 
Ale.xandria, La 
Trinity, Tex... 
Corsicana, Tex. 
Victoria, Tex.. 



June 17-29, 1908 
July 29, 1908... 
Aug. 24,1907... 
Sept. IS, 1906... 
Jan., 1909 




14.4 
9.09 
8.3 
5.9 

5.74 



IN HANGING BOLLS. 



Denison, Tex 

Calvert, Tex 

Goliad, Tex 

Do 

San Antonio, Tex. 

Victoria, Tex 

Natchez, Miss 

Marshall, Tex 

Trinity. Tex 

Waco, Tex 



Aug. 27, 1907. 
Aug. 23, 1907. 
July 28, 1908.. 

do 

July 24, 1908. 
Aug. 10, 1907. 
Jan., 1909.... 
Aug. 22, 1906. 
Aug. 9, 1906.. 
Sept. 20, 19011. 




36.3 

30.0 

26.31 

26.31 

25.71 

22. 7 

1I4 

13.5 

12.0 

11.8 



These records give merely the highest percentages for each State 
in each year. There are many other records which might be included 
between the above iiiriires. 



Highest records of total insect control of the boll weevil. 
IN FALLEN SQUARES. 



Athens, Tex 

Hallettsville, Tex. 

Overton, Te.x 

Beeville, Tex 

Victoria, Tex 

Bee\'ille, Tex 

Cuero, Tex 

Goliad, Tex 

Vidalia, La 

Sherman, Tex 



Locality. 



Date. 



Aug. 1,1907.. 
Aug. 1,1908.. 
Aug. 1,1906.. 

do 

July 29, 1908.. 
Sept. 1, 1906.. 
June 20, 1908. 
Aug. 28, 1908. 
Sept. 15, 1908. 
July, 1909.... 





Percent- 


Number 


age of 


of stages. 


Insect 




control. 


255 


96.11 


100 


92.00 


197 


85.20 


1,310 


78.80 


375 


78.38 


678 


77.40 


549 


73.60 


114 


66.69 


142 


61.20 


171 


49.71 



24 



INSECT ENEMIES OF THE BOLL WEEVIL, 



nighest records of total insect control of the boll weevil — Continued. 
IN HANGING SQUARES. 



Locality. 



Date. 



Number 
of stages. 



Percent- 
age of 
insect 

control. 



Athens, Tex 

Arlington, Tex. 

Dallas, Tex 

Victoria, Tex. . . 

Waco, Tex 

Mansfield, La... 
Victoria, Tex. . . 



Aug. 1,1907.. 
July, 1909.... 

do 

July 29, 1908. 
July 1, 1906.. 
Sept. 1, 1906.. 
Aug. 1, 1907.. 



75 
55 
57 
87 
99 
244 
253 



84.00 
75.44 
69.99 
58. 54 
56.56 
50.90 
50.00 



IN HANGING BOLLS. 



Mansfield, La. 
Waco, Tex... 
Overton, Tex. 
Mansfield, La. 



Sept. 29, 1906. 
Aug. 1, 1906.. 

do 

Sept. 24, 1906. 




58.30 
42.04 
40.50 
33.00 



THE CORRECT BASIS FOR COMPARISON OP MORTALITY STATISTICS. 

As has been explained, the examinations have been made from 
various sources. It is therefore necessary to arrive at some true 
basis for the comparison of these data before an exact knowledge of 
the conditions existing can be obtained. The first mortality of the 
weevil is that due to proliferation. Dr. Hinds, in Bulletin 59 of 
this bureau, has shown that the average mortality of weevil stages 
in squares from proliferation is 13.5 per cent and that the average 
mortality in bolls is 6.3 per cent. In the absence of further data 
these two percentages are used as a basis for obtaining the weighted 
average mortality. 

As nearly as the proportion can be estimated throughout the entire 
season, 15 per cent of the weevil stages are to be found in bolls and 5 
per cent in hanging forms. Wliether these arbitrary estimates be 
true or not, this is the only manner in which it will be possible to 
compare the mortality by the different factors in the various years. 
On this basis, therefore, a series of hypothetical tables has been 
erected. 

In order to show how the hypothetical average differs from the 
average obtained from the total examinations, two tables are given 
for each year, the first being a table giving the actual conditions in 
the four classes of infested material and the second table being a 
hypothetical table based upon 10,000 weevil stages on the arbitrary 
basis of 5 per cent of the stages in hanging forms and 15 per cent of 
the stages in bolls. The process continues by first subtracting the 
mortality by proliferation and then computing the mortality from 
climate, predators, and parasites from the remainder. The percent- 
ages of mortality given in the total line are based upon the total of 
10,000 stages. 



SHARE OF INSECT CONTROL IN WEEVIL MORTALITY. 



25 



1906. — The data on the mortahty of the wee\al in 190G may tliere- 
fore be condensed and tabulated as follows: 



Table VII. — Boll-weevil mortality in 1906. 





Number of 
weevil 
stages. 


Percentage 

of stages 

alive. 


Percentage of stages killed by- 


Total per- 
centage of 
mortality. 


Class of forms. 


Climate. 


Predators. 


Parasites. 


Hanging bolls 


5,452 

4,n8 

4,969 

25.534 


66.59 
46.20 
64.53 
34.80 


10.98 
20.30 
13.34 
31.20 


16.52 
20.50 
19.01 
30.70 


5.90 

13.00 

.90 

3.30 


33 41 




53.80 


Fallen bolls 


35 47 




65.20 






Totals and averages 


40,073 


44.19 


25.15 


26. 31 


4.31 


55.81 



Table VIII. — The hypothetical or iceighted average mortality of the boll weevil, 1906. 





o 

a 
.a 

6 

G 


to 


1906— Mortality from— 




Prolifera- 
tion. 




Climate. 


Predators. Parasites. 


Total. 


Class of fonns. 


^ 




^_^ 




.-, 




^ 










o 






o 


-d 


o 


-g -o . 


£ 


o 


































6C 


o 




2 


Q) 


Pr-S 


s 




3 




3 


?. • 






P 


6 




1 


a 

s 


c3 a 
? E 




a a 
a'i 


a 


C3 S 




c o 


a 










3 


m 




3 


S >- 


3 












Ph 


^Z 


fe 


^ 


« 


P-, 


IS 


P-i 


;z; jc^ 


^ 




:? 


Hanging bolls 


0.75 


75 


6.30 


4.7 


70.3 


10.98 


7.7 


16. ,52 


11.6 5.90 


4.1 


37.4 


28.1 


Hanging squares 


4.25 


425 


13. 50 


57.4 


367.6 


20. 30 


74.6 


20.50 


75. 4 13. 00 


47.8 


60.0 


255.2 


Total hanging.. 


5.00 


500' 


62.1 


437.9 




82.3 




87.0 


51.9 




283.3 


Fallen bolls 


14.25 


1,425| 6.30 


90.0 


1,335.0 


13 34 


178.1 


If* 01 


253.8 


.90 


T^ 


37.4 5.33.9 


Fallen squares 


80.75 


8,075113.50 


1,090.1 


6,984.9 31.20 


2,179.3 


30.70 


2,144.4 


3.30 


230.5 


69.S'5,644.3 


Total fallen 


95.00 


9,500! 


1,180.1 


8,319.9 


2,357.4 




2,398.2 


242.5 


6,178.2 


Totals and aver- 




1 








1 1 






ages 


100. 00 


10,000 


12.42 


1,242.1 




24.39 


2, 439. 7 


24.85 


2,485.2 


2.94 


294.4 


04.61 


6,461.5 



1 Given 10,000 weevil stages. 

1907. — The mortality during 1907 was 54.27 per cent when figured 
from the total number of stages and total mortality, thus showing a 
decrease of 1.54 per cent from the mortality of 1906 figured in the 
same manner. The parasitism sliowed an increase of 4.01 per cent. 



Table IX. — Boll-weevil mortality in 1901 



Class of forms. 


Number of 
weevil 
stages. 


Percentage 

of stages 

alive. 


Percentage of stages killed by- 


Total per- 
centage of 
mortality. 


Climate. 


Predators. 


Parasites. 


Hanging bolls 


431 

2,612 

342 

10.020 


76.80 
51.40 
49. 42 
42.90 


8.58 
14.50 
31.28 
33.50 


3.02 
7.50 
14.91 
19.90 


11.60 
26.60 
1.46 
3.70 


''S 20 


Hanging squares. . 


48 60 


Fallen bolls 


50 58 




57 10 






Totals and averages 


13,405 


45.73 


29.06 


16.88 


8.32 


54.27 



26 



INSECT ENEMIES OF THE BOLL. WEEVIL. 



Following the plan adopted for the 1906 records these figures 
may be weighted for comparison with the earlier records. 

Table X. — The hypothetical or weighted average mortality of the loll ■weevil in 1907} 





6 
S 

n 
3 eg 

■w be 

O M 

bjO 

(S 

C 


1 

o 

a 


1907— Mortality from - 




Prolifer- 
ation. 


.g 

B 


Climate. 


Predators. 


Parasites. 


Total. 


Class of forms. 




•6 
Si 

3 

1 


o 

u 

2 

si 

Pn 


■6 

a 

3 

^5 


o 
u 


■6 
3 

s 

3 


o 

S'i 


1 
u 

E 

3 




ri 
% 

E 

3 
'A 


Hanging bolls 

Hanging squares 


0. 75 75 
4. 25 425 


C.30 
13.50 


4.7 

57.4 


70.3 
367.0 


8.5S 
14.50 


6.0 
53.3 


3.02 

7.50 


2.1 

27.7 


11.60 
26.60 


8.1 
97.8 


29.70 
55.50 


20.9 
236. 2 


Total hanging . . 


5. 00 500 




02.1 437.9 


59.3 


29.8 




105.9 




257. 1 


Fallen bolls 

Fallen squares 


14. 25 
80.75 


1,425 
8,075 


6.30 
13.50 


90.0 
1,090.1 


1,335.0 31.28 
0,984.9 33.50 


417.6 
2, 339. 6 


14.91 
19.90 


199.0 
1,389.8 


1. 46 
3.70 


19.5 

258. 4 


50.90 
62. 80 


726.1 
5,077.9 


Total fallen 


95.00 9,500 




1,180.1 


8, 319. 9 




2.757.2 




1,588.8 




277.9 




5,804.0 


Totals and aver- 
ages 


1 
100.00 10,000 

i 


12.42 


1.242.1 




28. IG 


2,816.5 


10.18 


1,618.6 


3.83 


383. 8 


GO. 61 


6,001.1 



1 Given 10,000 weevil stages. 

This table shows a weighted increase of 0.89 per cent for parasites 
and a weighted decrease of 4 per cent for all agencies due to the 
falling off in control by predators. 

1908. — The mortality during i90S was 44.84 per cent when figured 
from the total number of stages, the total mortality thus shomng 
a decrease of 9.93 per cent from 1907. The parasitism showed an 
increase of 1.68 per cent. 

Table XL — Boll-weevil mortallhi'in 11/08. 





Number of 
weevil 

stages. 


Percentage 

of stages 

alive. 


Percentage of stages killed by- 


Class of forms. 


Climate. 


Predators. 


Parasites. 


All agen- 
cies. 




1,8.39 

5,922 

941 

20,844 


49.40 
49. 01 
70. 25 
57.28 


38.48 
19.24 
20. 08 
20.30 


3.97 
9.80 
5.95 
15.18 


8.15 
21.70 
3.71 

7.15 


50.60 


Hanging squares 


50.99 


Fallen bolls 


29.75 




42.72 






Totals and averages 


29, 546 


55. G6 


21.21 


13.12 


10.00 


44.34 



SHARE OF INSECT CONTROL IN WEEVIL MORTALITY. 



27 



Following the plan adopted for the 1906 and 1907 records these 
figures may be weighted for comparison with the earlier records. 

Table XII. — The hypothetical or veighted average viortahty of the boll weevil in 1908.^ 





6 

R 




1908— Mortalily from — 




Prolifer- 
ation. 




Climale. 


Predators. 


Parasilos. Total. 


Class of fonns. 


F? 


ac 


^ 






<-H 




<- 


,^ 




*« 
















o 


■73 


o 


-a 


o 


T3 


o 








M 








l_* 






Q^ 


j_j 


^ 








0) ° 








«- 






O 4J 














60 




b«_' 


M 






M 


So-o 


M 






§£-• 


M 




a 


E 

3 


a o 


1 


.g 

B 

at 


a 2 


E 


s a 
il 

0) fc. 


a 


a g 

ii 


s 

3 


S2 

C O 

2 


a 

3 




Pi 


2; 


Ph 


z 


A 


Ph 


2; 


p^ 


1 


Ph 


12; 


Ph 


Z 


Hanging bolls 


0.75 


75 6.30 


4.7 


70.3 


38.48 


27.1 


3.97 


1.4 


8.15 


.5.7 


.51.80 


38. 9 


Hanging squares 


4.25 


425,13.50 


57.4 


307.6 


19.24 


70.7 


9.80 


30.0 


21.70 


79.8 


57.30 


243.9 


Total hangiag.. 


5.00 


500 


62. 1 


437.9 




97.8 




37.4 




85.5 




282.8 


Fallen bolls 


14.25 


1,425 6.30 


90.0 


1,335.0 


20.08 


268. 1 


5. 95| 79. 4 


,3.71 


49.5 


.34. 10 


487.0 


Fallen squares 


80.75 


8,075 13.50 


1,090.1 


0,984.9 


20.301,417.9 


15. IS'I.OOO. 3 


7.15 


499. 4 


50.30 


4,007.7 


Total fallen 


95.00 


9,500 


I.ISO. 1 


8,319.9 


|1, 686.0 


1,139.71 548.9 




4,554.7 


Totals and aver- 




i 






1 


1 1 1 






ages 


100.00 


10,00012.42 

i 


1,242.2 




17. 83 1, 783. 8 11. 77jl, 177. ij 6. 34 634. 4 


48.37 


4,837.5 



1 Given 10,000 weevil stages. 

This table shows a weighted increase of 2.51 per cent for parasites 
and a weighted decrease of 12.24 per cent for all agencies, due to 
the falling off in control by both climate and predators. 

1909. — The mortality during 1909 was 41.73 per cent wlien figured 
from the total number of stages, the total mortality thus showing 
a decrease of 2.61 per cent from 190S. Tlie parasitism showed 
also a decrease amounting to 4.6S per cent. 

Table XIII. — Boll-weevil viortality in I'jO'.i. 





Number of 
weevil 
stages. 


Percentage 

of stages 

alive. 


Percentage of stages killed b 


y— 


Class of forms. 


Climate. 


Predators. 


Parasites. 


All agen- 
cies. 


Hanging bolls 


1,534 

1,959 
573 

7,587 


53.33 
61.16 
54.82 
58.79 


37.94 
12. 96 
27.74 

26. 58 


5.21 
6.38 
1.5.00 
12. 39 


3. .52 
19.49 
2.44 
2.24 




Hanging squares 


38.84 


Fallen bolls 


Fallen squares 


41.21 




Totals and averages 


11,653 


58. 27 


25. S4 


10. 56 


5.32 


41.73 



28 



INSECT ENEMIES OF THE BOLL WEEVIL. 



Following the plan adopted for the three preceding years these 
figures may be weighted for comparison with the earlier records: 

Tablk XIV. — Tlie hypothetical or weighted average mortality of the boll weevil in IbO'j.^ 





u 

a 

a 
ft 

O M 

<o ^ 

bo 

C3 

C 


1 
o 
t-. 

S 
3 
'A 


1909— Mortality from— 




Prolifer- 
ation. 


.g 
i 


Climate. 


Predators. 


Parasites. Total. 


Class of feriiis. 


o 
o 

CO 

1 


■3 

'Sa 

o 

e 

3 


o 

Si 

Ph 


•6 

a 

3 


"o 

§a 


r3 

a 

3 

a 

3 


o 
u 

g"l 

Ph 


-73 

a 

3 


o 

a* . 

a o 


3 

a 

3 


Hanging bolls 

Hanging squares 


0. 75 

4. 25 


75 
425 


6.30 
13.50 


4.7 
57.4 


70.3 

367.6 


37.94 
12.96 


20.7 
47.6 


5.21 
6.38 


3.7 
23.4 


3.52 
19.49 


2.5 
71.6 


50. 13 
47.29 


37.6 
200.0 


Total hanging. . 


5.00 


500 




62.1 


437.9 




74.3 




27.1 




74.1 




237.6 


Fallen bolls 

Fallen squares 


14.25 
80.75 


1,425 
8,075 


6.30 
13.50 


90.0 
1,090.1 


1,335.0 
6,984.9 


27.74 
26.58 


370.3 

1,856.6 


15.00 
12.39 


200.2 
805. 4 


2.44 
2.24 


32.6 

156. 5 


48.63 
49.14 


693.1 
3,968.6 


Total fallen 


95.00 


9,500 




1,180.1 


8,319.9 




2,226.9 




1,06.5.6 




189.1 




4,661.7 


Totals and aver- 


100. 00 


10,000 


12.42 


1,242.2 




23.01 


2,301.2 


10.f92 


1,092.7 


2.03 


263.2 


48.99 


4 899 3 







1 Given 10,000 weevil stages. 

This table shows a weighted decrease of 3.71 per cent for parasites 
and a weighted increase of 0.62 per cent for all agencies due to an 
increase in climatic control. 

In the following table is given a comparison of the weighted aver- 
age control by all agencies for the four years. 

Table XV. — Weighted average mortality of the loll weei'il, Vj06-li)0l). 





Weighted average mortality due to— 


Years. 


Prolifera- 
tion. 


Climate. 


Predation. 


Parasites. 


All agen- 
cies. 


1906 


12.42 
12.42 
12.42 
12.42 


24. 39 
28.16 
17. S3 
23.01 


24.85 
16.18 
11.77 
10.92 


2.94 
3.83 
6.34 
2. 63 


64 61 


1907 


60 61 


190S 


48.37 


1909 


48 99 






Average 


12.42 


24.45 l.^O.-i 


3. 93 


56 73 











In view of the fact that certain cotton varieties retain the infested 
squares more than others, it is interesting to make another hypothesis 
on the basis that 50 per cent of the infested forms are hanging. The 
year 1908 is chosen to illustrate this phase of the subject. 



SHARE OF INSECT CONTROL IN WEEVIL MORTALITY. 



29 



Table XVL — A hypothetical average mortality of the boll weevil in square-retaining 

varieties.^ 





z 
a 

3 

a 

^1 

•ol 

B 
a 

o 


1 
1 
"3 

a 
1 


1908. Mortality from— 


Class of forms. 


Prolifera- 
tion. 


-a 

a 


Climate. 


Preda- 
tors. 


Parasites. 


Total. 


o 

^^ 

"S5 

Ph 


3-^ 


o . 




C3T3 

rj C3 

Ph ^ 


0) 

3-^ 


o . 

o n 


S3 

3-^ 

57.3 
797.8 


o 


u 

o 

3-^ 


Hanging bolls 

Hanging squares 


7.50 
42.50 


750 
4,250 


6.3 
13.5 


47.2 
573.7 


702.8 
3, 676. 3 


38.48 
19.24 


270.4 

707.3 


3.97 
9.80 


27.9 
360.3 


8.15 
21.70 


53.7 
57.3 


402.8 
2, 439. 1 


Total hanging.. 


50.00 


5,000 




620.9 


4,379.1 




977.7 




388.2 




855.1 




2,841.9 


Fallen bolls 


7.50 
42.50 


750 
4,250 


6.3 
13.5 


47.2 
573.7 


702.8 
3, 676. 3 


20. OS 
20.30 


141.1 
746.3 


5.95 
15.18 


41.8 
558. 1 


3.71 
7.15 


2(;.l 
262.8 


34.1 
50.3 


256 2 


Fallen squares 


2,140.9 


Total fallen 


50.00 


5,000 




620. 9 


4,379.1 




887.4 




599.9 




288.9 




2,397.1 


Totals and aver- 


100.00 


10,000 




1,241.8 




18.65 


1,865.1 


9.88 


988.1 


11.44 


1,144.0 


52.39 


5 239 











1 Given 10,000 weevil stages. 

This series of tables, wherein the mortaUty of the weevil is given 
an accurate basis for comparison, brings to light some very important 
points. This is especially the case in Table XVI, which is based 
upon the hypothesis that 50 per cent of the infested forms are hang- 
ing. By comparing this hypothesis for the year 1908 with the 
table of the same year in which it is considered that only 5 per cent 
of the forms are hanging, it will be noticed that under the condition 
of the greatest proportion of hanging squares the total control of the 
weevil would be 52.39 per cent and the number of parasites to 10,000 
weevil stages would be 1,154; whereas, with the smaller proportion 
of hanging forms, the total control of the weevil would be 48.37 per 
cent and the total number of parasites 634 to 10,000 weevil stages. 
Now this shows a gain of 4 per cent in the actual control of the 
weevil and almost double the number of parasites to 10,000 weevil 
stages. Naturally, under such conditions it would follow that the 
parasitic control would be even higher than that which has been used 
as a basis for the estimate and would increase in rapid proportion. 
In view of tliis showing of the fact that the larger the proportion of 
hanging squares to the entire amount of infested forms, the larger 
the insect control becomes, we recommend that those who are inter- 
ested in the breeding of cotton varieties attempt to secure varieties 
of cotton which will combine the necessary quahties of productive- 
ness, length of lint, and early maturing mth the square-retaining 
tendency. It may be pointed out that the varieties known as Rublee 
and Cook's Improved are not only conspicuous for the square-retain- 
ing ciualities but also for their desirabiUty under boll-weevil condi- 



30 INSECT ENEMIES OF THE BOLL WEEVIL. 

tions. Several other varieties have been noticed to have this 
same tendency, but they have not the other characteristics to recom- 
mend them. In this connection we refer the reader to section 4 
(p. 21), in which it has been shown that at least two States have had 
a higher average control of the boll weevil in hanging squares than in 
fallen squares when all of the records available are considered. It 
wdll also be noticed in section 5, under Table XI, giving the actual 
control of the boll weevil in 1908, that hanging squares and hanging 
bolls were decidedly in the lead in the total control over either fallen 
squares or fallen bolls. While tliis has not been the case in the other 
years under consideration, we nevertheless consider that the pres- 
ence of a nursery for the parasites in the field is most desirable. 
Undoubtedly these hanging squares constitute such a nursery. 

6. A STUDY OF HOW AGRICULTURE MODIFIES INSECT CONTROL. 

From studies made during 1907 the follomng comparisons may 
be made to show the number of factors that it is actually necessary 
to consider in order that differences in parasitism ma}' be understood. 

At Arlington, Tex., records were kept on a field in the red loam 
post-oak country or "cross timbers," another in the Trinity River 
bottoms, and a third on the l)lack waxy prairie. The first was 
planted March 12, the second April 1, the third April 5. On August 
28 the weevil infestation of squares in the timbers was 80.5 per cent, 
in the bottoms 94.3 per cent, and on the prairie 21.4 per cent. At 
the same time the parasitism in fallen squares on the timbers was 3.12 
per cent, in the bottoms 1.9 per cent, and on the prairie 2.56 per cent. 
In the timbers the parasitism of hanging squares was 39 per cent and 
in the bottoms 24.78 per cent. The variable factors are soil, flora, 
time of planting, variety of cotton, and weevil abundance. Hang- 
ing squares were found in 1906 to be more highly parasitized in 
timber land than on the prairie, and fallen squares inversely. There 
appears to be an indication of the value of early planting. This 
first field was the earliest field known in the vicinity and it showed 
a high parasitism in hanging forms throughout the season. 

At Calvert, Tex., were two fields on the prairie, one planted March 
11 and 12, the other April 1. On June 21 the weevil infestation of the 
first was 18 per cent and of the second 21 per cent. On July 5 the 
parasitism in the first was 2 per cent and in the second nothing. 

At Denison, Tex., were two fields, one in the red clay, the other on 
sandy loam, neither surrounded by timber. On the first the stalks 
were burned February 28, on the second March 15. Both were 
planted IMarch 30. On August 27 the weevil infestation on the 
first was 88.3 per cent, on the second 87.6 per cent; the parasitism in 
fallen squares on the first was 6.31 per cent, on the second 2.85 per 



HOW AGEICULTUEE MODIFIES INSECT CONTROL. 31 

cent; the parasitism in hanging squares on the first was 5.79 per 
cent, on the second 11.53 per cent. Here the only variable condi- 
tions were soil, possibly weeds, and time of phmt destruction. The 
parasitism in the two classes of forms was diametrically reversed. 

At Terrell, Tex., were two fields on the sandy prairie, both planted 
in March, but having diflerent weeds present. The weevil infesta- 
tion August 26 on one was 65.2 per cent, on the other 97.5 per cent, 
while the parasitism in hanging squares on the first was 29.5 per cent 
and on the second 25.6 per cent. The variables were field siu'round- 
ings and weevil abundance. 

The unknown influence which entered most of these examples was 
very probably tlie relative abundance of the diflerent species of para- 
sites. This may best be illustrated by the hanging squares from the 
timbers and bottoms at Arlington, which are quoted above. In the 
timbers the tleterminable parasites proved to be 16 Eurytoma tyloder- 
matis, 10 Microhracon tnelUtor, 6 Ceramhycohius cyaniccps, 5 Micro- 
dontoments anthonomi, and 3 Catolaccus spp. In the bottoms there 
were 17 Ceramhycohius cyaniceps, 13 Microdontomenis anthonomi, 10 
Eurytoma tylodermatis, S Catolaccus spp., and 7 Microhracon mellitor. 
The rank of the species was almost entirely reversed. 

Probably the most important point in the entire set of examples 
is that the earliest crop had the most parasites. To show this in 
another way we may refer to the conditions on the experimental farm 
at Dallas. The first part of the field to put on squares was the first 
part to show ])arasites. On July 8 infested squares were to be found 
in six plats, but only on this earliest plat was there any parasitism — 
5.7 per cent. On July 19 it and the adjacent plat were still consid- 
erably in the lead. 

That the earliest field should show the highest imrasitism was 
expected by the writers in view of the early spring observations. 
The parasites in hibernation, whether on the boll weevil or on winter 
cohosts, all reached maturity in the latter half of March at Dallas. 
It was reasoned that cotton, squaring and attacked by April 15, 
would get the hibernated parasites in any ])art of the State; that 
cotton squaring and attacked by ]May 15 would get the first genera- 
tion of parasites from the cohosts, and so on. It is reasonable to 
expect that cotton with squares infested in season to attract hiber- 
nated parasites or a new brood from cohosts will fare better than 
cotton that commences squaring when all the parasites are concen- 
trated upon neighboring cohosts. This cotton must wait until the 
period of the favored cohosts begins to wane before the parasites will 
begin to seek new scenes of activity. Although it was so reasoned, 
it was hardly expected that there would be sufficient proof to warrant 
voicing the proposition. 



32 



INSECT ENEMIES OF THE BOLL WEEVIL. 



A series of examinations was made in the vicinity of Victoria, 
Tex., in 1907 and 1908. On October 9, 1907, Mr. Cusliman noted 
that fall destruction of the cotton was being carried on quite exten- 
sively, but in different manners. On the east side of the river, south 
and east of town, was an area in which practically all of the cotton 
had been defoliated by the cotton leaf-worm. This area was sepa- 
rated by the river and by a wide strip of huisache timber from 
other cotton areas. In other directions were located fields stripped 
by grazing, some that were plowed under, and one field only was 
found which had received no treatment. 

On June 17, 18, and 19, 1908, fallen squares fi-om several of these 
fields were examined, with the following results: 

Table XVII. — BoU-ivccvil mortality in various cotton fields, Victoria, Tex., 1908. 



Treatmenl , 1907 



Total 

stages. 



Total. 



Perceutage of mortality, 1908. 



Climate. 



Predar 
tors. 



Parasites. 



Destroyed stalks, September 

Plowed, October 

Plowed, December 

Grazed, October 

Do 

Defoliated 

Do 

Do 



314 

296 
354 
144 
290 
480 
513 
375 



IS. 18 
13.80 
61). 70 
44.40 
37. 50 
29. 30 
52.80 
23.70 



5.43 
7.70 
14.40 
24.30 
25.50 
20. 60 
27.00 
16.50 



4.14 
3.00 
41.20 
15.97 
7.20 
2.50 
11.10 
3.10 



9.23 
3.00 
5.08 
4.16 

4.80 
6.20 
14.40 
4.50 



These strildng differences in the ])ercentage of control can not be 
attributed to the differences of treatment in 1907, although that 
may have had a bearing. The different fields had different weeds 
and plants surrounding them, they received dift'erent treatment in 
the spring of 1908, and there are many other reasons why no one 
basis of comparison can be chosen. The table is offered to illustrate 
how wide a dift'erence in natural control can be found in fields only a 
few miles apart and proves conclusively the value of individual effort 
in the fight against the weevil. 

Numerous other instances are contained in the notes that are quite 
as strildng as the one to which reference has been made. There is 
every reason why each planter should follow out as complete a pro- 
gram against the weevil as he can, because each efl'ort reduces the 
total infestation of his neiaiiborhood. 



7. CLIMATIC CONSIDERATIONS. 

The climate of the hibernating season of 1906-7 was very unusual, 
so much so that the boll weevil hardly became quiescent, and the 
emergence was largely during March, whereas normally it is in 
April. The boll-weevil parasites mature simultaneously with the 



CLIMATIC CONSIDEKATIONS. 33 

great wave of boll-weevil emergence. A glance at the accompanying 
diagrams (figs. 4, 5) will show that in Louisiana the monthly mean 
temperature was from 3° Fahrenlieit (November) to 10° (January) 
higher than the normal, and in Texas it varied from normal 
(November) to 10° above normal (March) durmg the entire winter. 
On the other hand, the accumulated moisture from November 1, 
1906, to March 1, 1907, in Louisiana was 5 inches below normal and 
in Texas 1 inch below normal. 

Cotton was planted in March and April (1907) and normally would 
have squared in May and June, but it was retarded a month by the 
low temperature in April and May, during which months the monthly 
mean temperature was 2° to 3° below normal in Louisiana and 
3° to 6° below normal in Texas. In adcUtion to the cold of the 
spring, the precipitation in Louisiana from March 1 to July 1 
was 7 inches above the normal and in Texas 2 inches above. This 
cold and the presence of volunteer cotton tided the boll weevil over 
until the planted cotton was up. The parasites were obliged to seek 
cohosts from March 15 until late in May or in June. The cold, damp 
weather undoubtedly retarded their development so that the first 
generation was ready to attack such boll weevils as were breeding 
late in May and early in June. As only a few fields held this advan- 
tage to the parasites, these fields naturally became much better 
stocked with parasites, as has been pointed out in another paragraph. 

The summer and early fall months showed a slight deficiency in 
rainfall and a slightly higher mean temperature — to such an extent, 
however, that the season was considered dry, for the cotton did not 
put on a very luxuriant foliage, and thus gave the sun plenty of play 
on the fallen squares. The result is evidenced by the high percentage 
of mortality from heat shown in the mortality tables. The increase 
in parasitism may be ascribed to the same cause. 

The mean temperature of October, 1907, was normal in Texas, but 
10° above normal in Louisiana. This warm season was followed by 
a very sudden drop in temperature on November 11, the ''norther" 
lasting until the 15th. This caused the November mean in both 
States to be 3° below normal (Texas 53° F., Louisiana 56° F.). In 
both States during this one month the precipitation was 3 inches 
above the normal. In northern Texas about 30 per cent of the adult 
weevils were killed by cold. The temperature at Dallas ^ reached 
14° on November 13, which was 11° colder than was experienced in 
1906 and 21° lower than at any time in November, 1905. The boll 
weevils were not prepared for this cold, as they were still in great 

1 The record was made both by the minimum thermometer and the self-registering thermograph at the 
laboratory in East Dallas, and is a few degrees lower than the official record at Oak Cliff, about 5 miles 
to the west and across the Trinity River. 

16844°— Bull. 100—12 3 



34 



INSECT ENEMIES OF THE BOLL WEEVIL. 



numbers on the plants and many immature stages were developing 
in green squares and bolls. 

Table XVIII gives the results of the examinations made immedi- 
ately after the freeze. 

Table XVIII. — Mortality of the boll weevil in Texas, November, 1907. 





Date. 


Form. 


Location. 


Condi- 
tion. 


Stages. 


Mortal- 
ity. 


Mortality due to- 


Place. 


Cold. 


Para- 
sites. 


other 
causes. 


Dallas 


1907. 
Nov. 14 
.do .... 


Squares... 
...do 


Fallen.. 
...do..... 


Green... 

Dry 

Green... 

...do 

...do 

.^7o.-.::: 

Green. . . 

Mixed... 

...do 

...do 

...do 


93 

151 

2 

(1) 
13 

8 
7 
56 
21 
16 
27 


Per ct. 

97.7 
47.0 
100.0 
100.0 
100.0 
30.7 
37.5 
100.0 
96. 3 
95.2 

ioo:o 

100.0 


Per ct. 
96.7 
36.4 
100.0 
100.0 
100.0 
7.6 


Per ct. 
1.0 
5.9 


Per ct. 


Do 


4.6 




Nov. 15 
Nov. 19 
Nov. 20 
Nov. 14 
do 


...do 

...do 

..do 


Plant... 

...do 

...do 










Calvert 






Dallas 


Bolls 

...do 

...do 

...do 

...do 

...do 

...do 


Fallen... 

Plant.... 

...do 

...do 

...do 

...do 

...do 


7.6 


15.3 


Do 


37.6 




Nov. 15 
Nov. 19 
Nov. 20 
Nov. 21 
...do 

} 


ioo.o 

57. i 
38.0 
50.0 
63.0 






Navasota 


3.5 


35.7 

57.2 




50.0 


Hillsboro 


37.0 




246 
148 


66.3 

88.5 


59. 8 
49.3 


4.0 
2.0 


2.8 


averages. 


\Bolls 






237 1 












Totals and 


394 


74.3 


55.3 


3.2 


15.8 















1 Several. 

2 Most of the death from "other causes" in bolls was due to proliferation, which seems to be stimulated 
by frosts. 

From this small number of stages no general statement can be made. 
Of the 394 stages 55.3 per cent were killed by cold. Of the stages 
in green squares or bolls, 98 per cent were killed by the cold. 

The most interesting point is that although 98 out of 100 weevil 
stages in green forms were killed, a parasite larva was found to have 
just hatched from its egg on a weevil larva killed by cold. Three 
other similar cases were found in dry forms. Seventeen cases of 
parasitism were found on the 394 stages. Among these were two 
living eggs of which one was an entirely new type and also two pupse 
which proved to be Hahrocytus inercei. 

The remainder of the winter of 1907-8 — that is, from December to 
March 1 — had a mean temperature a few degrees above the normal, 
but with several severe cold spells. During the four winter months 
the precipitation in both States was above the normal. The short 
cold spells with warmer intervening weather and heavier rainfall 
were disastrous to the boll weevil. The February examination to 
ascertain the mortality of the weevil indicated about 98 per cent 
mortality. As a result of the extreme scarcity of weevils in the spring 
and summer in most parts of Texas, there was a great reduction in 
the number of parasites. In fact, in the northern portion of the 
Texas black prairie the parasites were forced to seek other hosts. A 
kiUing freeze in November, 1908, agam killed many boll weevils. 



HOW INSECT CONTROL FOLLOWS WEEVIL. 85 

Following the cold of November, 1908, the winter was unusually 
warm, being at least 5° F. above the normal in both Louisiana and 
Texas. From March 15 to July 15, in both States, the temperature 
was almost normal. However, by this time there was an accumulated 
tleiiciency of precipitation in each State of several mches. The 
months of July and August m Texas were extremely warm and many 
places recorded the maximum temperatures for their entire ])eriod 
of records. While the heat was less excessive in Louisiana, it never- 
theless reached very high points. This extreme weather during these 
two months had a tremendous effect upon the boll weevil and upon 
its parasites, although records taken after some of the hottest days 
showed that the mortality of the boll weevil from the heat was con- 
siderably higher than the mortality of the parasites of the boll weevil. 
After the middle of August a period of renewed growth of the cotton 
plant gave the boll weevil an opportunity for increased development 
and consequently permitted a large number of weevils to mature 
before the hibernation season. Incidentally with this fall brood of 
weevils, we find that there was a very great uicrease m the parasites, 
especially m Louisiana. The followmg two diagrams (figs. 4, 5) 
illustrate the temperature of the years under consideration. 

8. HOW INSECT CONTROL FOLLOWS THE DISPERSION OF THE BOLL 

WEEVIL. 

From an economic standpomt it is very important to know what 
kind of natural control of the boll weevil can be expected in newly 
invaded country. Since 1904 it has been noticed that maxmium 
infestation is generally reached by August 1, and that smiultaneously 
an extensive dispersion of the boll weevil takes place. At this period 
the boll weevils fly to fields many miles beyond the parasites. The 
clunatic conditions during the dispersion period are such as will not 
seriously interfere with prolific breeding of the weevils in the newly 
infested territory. The extent of the dispersion is limited only by 
the number of weevils flymg and the amount of food supply available. 
In the fall of 1909 the sparse production of cotton m southern Missis- 
sippi brought about a dispersion of 120 miles into new territory. 

Our knowledge of the bisects which attack the boll weevil shows 
that most of them are derived from the parasites of similar weevils 
that are native to the region infested. Therefore, if parasites and 
predators are present m the mvaded region, it is reasonable to expect 
that they will immediately begm attacking the boll weevil. This 
assumption has been proven in many definite cases. At Minden, La., 
in 1906, a parasite larva was found in a green square infested by the 
first generation. At Roxie, Miss., where the weevils had been present 
only a few weeks in September, 1908, ant work and parasite work 



36 



INSECT ENEMIES OF THE BOLL WEEVIL. 



were easily found. Later in the season of 1908, an isolated infestation 
was found at Roadside, in Yazoo County, Miss., about 40 miles beyond 




the regular lifie of infestation, but it was noticeable that the weevil 
was parasitized m this particular field. 



STATUS OF WEEVIL AND CONTEOL BY INSECTS. 



37 



9. THE STATUS OF THE BOLL WEEVIL AND ITS CONTROL BY INSECTS. 

During the seasons of 1908 and 1909 the examinations of the boll 
weevil to determine its status demonstrated that there had been a 




tremendous falling off of the weevil in all western and northern Texas. 
In August, 1909, there was less than 10 per cent infestation in half of 



38 INSECT ENEMIES OF THE BOLL WEEVIL. 

Texas and in all of Oklahoma. At the same time a maxunum mfesta- 
tion was found in all of that part of Louisiana lying south of the Red 
River and m Mississippi for about 20 miles east of Natchez. An analy- 
sis of the parasite records for this same season shows that the parasite 
control of the weevU in these sparsely infested regions of Texas was 
very light, whereas the control in the heavily mfested regions of south- 
ern Louisiana and Mississippi was correspondmgly very high. The 
inference drawn from this observation is either that the boll weevil 
had ceased to be the predommating weevil species for parasitic 
attack m the lightly mfested region, or that the parasites had been 
destroyed by the heat. That the parasites were not all destroyed 
by the heat is demonstrated by many records of the same parasites 
on other species of weevUs durmg the fall and winter of 1909. 

10. A BRIEF STATEMENT OF THE VARIOUS CLASSES OF CONTROL EXER- 

CISED UPON THE BOLL WEEVIL. 

Before passing from this part of the report, which deals with the 
general conditions obtaining, it is necessary to say a few words con- 
cerning the classes of control which are of importance in repressing the 
boll weevil. The first agency which is responsible for mortality of the 
weevils is the resistance of the cotton plant to attack, evidenced either 
by the toughness of the plant tissues which must be punctured, or by 
the proliferation of the tissues, which destroys the weevil eggs and 
larvae by crushing. When the infested form falls to the ground or 
withers on the plant it becomes immediately a subject for numerous 
other factors of control. Intense heat kills many stages. A large 
number of parasite species seek out infested squares for their prog- 
eny; myriads of ants, beetles, and mites find nourishing food by 
merely cutting their way into the infested forms and devouring the 
weevil stages. Li addition to these, sudden cold freezes countless 
numbers of developing weevils. Neither are adults free from adverse 
conditions. Many are killed by heat, or cold, or drowning; many are 
picked up by birds and lizards or preyed upon by other insects; and 
finally multitudes are starved on account of the ravages of other 
insects upon their food supply. In this report we are able to deal 
only with the three factors which are determinable in the control of 
immature weevils, namely, climate, parasites, and predators. 

11. PRACTICAL CONCLUSIONS DERIVED FROM STATISTICAL STUDIES. 

The following conclusions of economic importance have been 
reached from a study of this large series of statistics : 

I. The month of August is the most important month for the con- 
trol of the weevil by insect enemies. As this month is also the most 



BIOLOGICAL COMPLEX. 39 

important in the control affected by climate, it should be considered 
as one of the most critical times of the year for controlling the boll 
weevil. When a sudden drop in the temperature below freezing 
occurs in the month of November before a large proportion of the 
weevils has entered hibernation, and while many are still immature, 
an excellent control of the species can be obtained. As, however, 
this is only an occasional occurrence, it can not be relied upon and 
every measure possible should have been carried out to prevent the 
weevils from gomg into hibernation at all. 

II. Hanging squares are the most important infested parts for the 
work of parasites, and fallen squares in a similar degree for the work 
of the predatory enemies. It has been demonstrated also that in 
certain years the total control by all agencies is greater in hanging 
squares than in fallen squares, and furthermore that in the more 
humid States this condition is the prevalent one. 

III. It has been shown by examples that the total mortality of 
the weevil can be increased m proportion as the number of hanging 
squares in a given area is increased and likewise that the pro- 
portion of parasites to weevils is increased. It is therefore recom- 
mended that plant breeders attempt to develop varieties of cotton 
which will retain the squares, but will also have the other desirable 
varietal characteristics necessary for the production of an early 
cotton crop. 

IV. The insect control of the boll weevil is dependent in a large 
measure upon the operations of the farm and for this reason all those 
field practices which have been included in the sj-stem of cultural 
control of the boll weevil are further recommended as tending to 
increase the insect control. 

PART II. BIOLOGICAL COMPLEX. 

In Part I of this bulletin one set of facts, composed of statistics, 
was dealt with, and it was merel}^ hinted that the causes of these con- 
ditions were very complex. In this part is presented another series 
of facts, even more significant than the fu"st, but much more difficult 
to present in a tangible manner. The study of these biological 
factors received its fu'st impetus when at Clarendon, Tex., in 1905, 
Mr. C. R. Jones and the senior author were fortunate enough to learai 
the biologies of tln-ee species of weevils and to find that all these were 
parasitized more or less abundantly by the same parasites as is the 
boll weevil. It was already known that some of the parasites of the 
boll weevil attacked other weevils, but the significance of this fact 
had not been realized. 



40 INSECT ENEMIES OF THE BOLL WEEVIL. 

With this simi)le beginning the search for other hosts of the boll- 
weevil parasites was started and we have now built up the knowledge 
of the following complex : 

Owmg to the complicated nature of the data to be presented in 
this part, these have also been arranged in the following sections : 

1. A list of the insect enemies of the boll weevil. 

2. The hosts of boll-weevil parasites. 

3. Mites which attack the boll weevil. 

4. Flies which parasitize the boll weevil. 

5. The hymenopterous parasites of the boll weevil. 

6. Biological notes upon the parasites of the boll weevil. 

7. The development of the parasites. 

8. The distribution of the parasites. 

9. The parasite seasons. 

10. Adjustment to new hosts. 

11. Beetles which prey upon the boll weevil. 

12. Lepidopterous larvae which are incidentally predatory upon 
the boll weevil. 

13. Ants which prey upon the boll weevil. 

14. Biology of the cohosts of the boll-weevil parasites. 

15. A list of the host plants of the cohost weevils. 

16. A summary of the most important biological facts. 

1. A LIST OF THE INSECT ENEMIES OF THE COTTON BOLL WEEVIL. 

The boll weevil is known to be attacked by 29 species of parasites, 
while 20 species of predators attack the immature stages and 6 
species of predators attack the adults. These species are listed as 
follows : 

Arachnida. 

Acarina. Sarcoptoidea. 
Tarsonemidae. Pediculoidinffi. 

Pediculoides ventricosus Newport (parasite on larva), Mexico. 
rcdiculoides sp. (parasite on larva), Louisiana, Texas. 
Tyroglyphidse. 

Tyroglyphus breviceps Banks (parasite on larva), Texas. 
Insecta. 
Orthoptera. Mantoldea. 
Mantidae. 
Stagmomanlis limbuta Ilahn (predator on adult), Texas. 
Hemiptera-Heteroptera. 
Reduviidse. 
Apiomerus spissipes Say (predator on adult), Texas. 
Coleoptera. Adephaga. 
Carabidaj. 

Evarthrus sodalis Le Conte (predator on adult), Louisiana, Texas. 
Evarihrus sp. (predator on adult), Louisiana. 



A LIST OF THE INSECT ENEMIES. 41 

Insecta — Continued . 
Coleoptera. Polyphaga. Diversiconiia. 
Cantharidse. 

Chauliognathus ST^yp. (predators on larva), Louisiana, Mississippi. 
Cleridae. 

Hi/dnocera pallipennis Say (predator on larva), Texas. 

Hydnocera pubescens Le Conte (predator on larva), Texas. 
Cucujidee. 

Cathartus cassiie Reiche (predator on larva), Texas. 
Lepidoptera. Bombycoidea. 
Noctuidse. 

Alabama argillacea Hiibner (defoliator, cuts off food supply). 
Hymenoptera. Formicoidea.' 
Dory lid 86. 

Eciton (AcaTnatus) commutatum Emery (predator on larva), Texas. 
Poneridic. 

Ectatomma tuberculatum Olivier (predator on adult) Guatemala. 
Myrmicidse. Cremastogasterinse. 

Cremastogaster Uneolata (Say) var. clara Mayr (predator on larva) Texas. 
Myrmicida-. Solenopsidinee. 

Solenopsis geminata (Fabricius) var. diabola Wheeler (j)redator on larva), 
Louisiana, Mississippi, Texas. 

Solenopsis molesta Say {=debilis Mayr) (predator on larva), Oklahoma. 

Solenoj)sis texana Emery (predator on larva), Louisiana, Texas. 
MyrmicidiE. Myrmicinai. 

Monomorium minimum Buckley (predator on larva), Louisiana, Mississippi, 
Texas. 

Monomorium pharaonis Linnaeus (predator on larva), Arkansas, Louisiana, 
Oklahoma, Texas. 

Pheidole sp. near Jlavens (predator on larva), Texas. 

Pheidole a'assicornis Emery (predator on larva), Texas. 
Dolichodcrida3. 

Forelius maccooH Forel (predator on larva), Texas. 

Dorymyrmex pyramicus Roger (predator), Cuba. 

Dorymyrmex pyramicus (Roger) vnT.JlaLms McCook (predator on larva), Texas. 

Iridomyrmex analis Andre (predator on larva), Texas. 
Formicidse. 

Formica fusca subpolita perpilosa WTaeeler (predator on adult), ]\Iexico. 

Formica pallidi-fulva Latreille (predator on larva), Arkansas. 

Prenolepis imparis Say (predator on larva), Arkansas. 
Hymenoptera. Chalcidoidea. 

Chalcididsi. Chalcidina?. Smicrini. 

Spilochalcis sp. (parasite), Texas. 
Torymidse. Monodontomerinai. 

Microdontomerus anthonomi Crawford (parasite), Louisiana, Texas. 
Eurytomida;. 

Eurytoma tylodermatis Ashmead (parasite), Arkansas, Louisiana, Mexico, Okla- 
homa, Texas. 

Bruchophagus herrerse Ashmead (parasite), Mexico. 

Eurytoma sp. (parasite), Texas. 

» All of these ants have been deterinined by Prof. William Morton Wheeler. 



42 INSECT ENEMIES OF THE BOLL WEEVIL. 

Insecta — Continued. 
Hymenoptera. Chalcidoidea — Continued. 
PerilampidtF. 

Perilampus sp.' (parasite), Louisiana. 
Encyrtidse. Eupelminee. 

Cerambycobius cyaniceps Ashmead (parasite), Arkansas, Louisiana, Mississippi, 
Oklahoma, Texas. 

Cerambycobius cushmani Crawford (parasite), Texas. 

Cerambycobius sp. (parasite), Mississippi. 
Pteromalidae. Pteromalinise. 

Catolaccus incertus Ashmead (parasite), United States. 

Catolaccus hunteri Crawford (parasite), Louisiana, Mississippi, Mexico, Texas. 

Habrocytus piercei Crawford, Louisiana, Texas. 

Lariophagus texanus Crawford (parasite), Texas. 
Eulophidtne. Tetrastichinae. 

Tetrastichus hunteri Crawford (parasite), Louisiana, Mississippi, Texas. 
Hymenoptera. Ichneumonoidea. 

Ichneumonidae. Pimplinge. Pimplini. 

Pimpla sp. (parasite), Texas. 
Braconidse. Sigalphinae. 

Sigalphus curculionis Fitch (parasite), Louisiana, Mississippi, Texas. 

Urosigalphus anthonomi Crawford (parasite), Texas. 

Urosigalphus schwarzi Crawford (parasite), Guatemala. 

Urosigalphus sp. (parasite), Texas. 
Braconidae. Braconinae. Braconini. 

Mia-obracon mellitor Say (parasite), Mexico, United States. 
Braconidae. 

Unknown species (parasite), Texas. 
Diptera. Cyclorrhapha. 
Phoridas. 

Aphiochssta nigriceps Loew (parasite), Texas. 

Aphiochseta fasciata Fallen (parasite), Texas. 

Aphiochseta pygmaca Zetterstedt (parasite), Texas. 
Tachinidie. 

Myiophasia xnea Wiedemann (determined by Coquillett) (parasite), Texas. 

Ennyomma globosa Townsend (parasite), Louisiana, Texas. 

HYPERPARASITES. '^ 

Dipteia. 

Plastophora (Pseudacteon) craivfordi Coquillett on Solenopsis geminata Fabriciua. 

2. THE HOSTS OF BOLL-WEEVIL PARASITES. 

As has just been stated, the boll weevil has 55 species of insects, 
which are known to attack it. Among the parasites are to be found 
7 which are occasionally accidentally hyperparasitic. At least 1 par- 
asite is known to attack one of the predators. The accidental preda- 
tor {Alabama argillacea) is attacked by 12 parasites, 46 predators, 

1 This species may be a parasite of a Chrysopa larva or of some lepidopteron wliich had entered a weevil 
cell. 

' The enemies of Alabama argillacea Hiibner afford some interesting sidelights on the complexity of the 
biological relations of cotton insects. 



MITES WHICH ATTACK THE WEEVIL. 43 

and 1 hyperparasite. Among these 46 predators are 6 which also 
prey upon the boll weevil. At least 1 very common predatory 
insect is known to prey upon many of the boll-weevil predators. 
Fifty-five species of weevils are known to be attacked as cohosts of 
26 species of parasites and of the 19 species of predators which attack 
the boll weevil. These 55 species of weevils are known to breed 
upon 91 species of plants, most of which are to be found in the vicinity 
of the cotton fields. Three of these weevils sometimes breed upon the 
cotton plant. Among the great number of parasites which attack 
the 55 coliost weevils, 44 species are definitely known to science and 
at least 6 species of hymenopterous parasites are known to attack 
these 44 species of parasites. This complexity could be carried still 
further, but probably enough has been stated to show how the many 
influences of nature are dependent upon one another. The state- 
ments are illustrated graphically in the accompanying diagram (fig. 6). 

The principal point of importance in all of these facts is that the 
boll weevil has been deriving its parasites from these 51 species of 
weevils and from other weevils wliich are not laiown to us, and 
there is every reason to believe that some of these other 44 species 
of parasites, or still additional ones to be discovered, may be drawn 
over to the boll weevil as parasites in the future. The weevils serv- 
mg as cohosts and the parasites are listed in the accompanying table 
(fig. 7) in such manner as to show the nature of the interrelationships. 

It mil be noticed from tliis table that 6 weevils, namely, Laria 
sallxi, Laria exigua, Smicraulax tuherculatus, Anthonomus alhopilosus, 
Tyloderma foveolatum, and Triclioharis texana each have 4 of the 
boll- weevil parasites; 4 weevils are attacked by 3 of the parasites, 
15 of the weevils by 2 parasites each, and the remaining 37 by only 1 
parasite each. 

Of the parasites, Ceramhycohius cyaniceps attacks 18 hosts, Eury- 
toma tylodermatis attacks 16 hosts, Catolaccus incertus 14, Catolaccus 
hunteri 13, and Microhracon mellitor 12. These 5 parasites are also 
regarded as the most important parasites attacking the boll weevil 
itself. Perhaps tliis unportance is due to the fact that they have 
a larger number of native hosts and are hence in greater abundance 
around the cotton fields than the parasites having fewer native 
hosts. 

3. MITES WHICH ATTACK THE BOLL WEEVIL. 
ACARINA. TARSONEMID^. 

The mites of the genus Pediculoides are assuming an important 
role among insect parasites, two species being accredited to the 
boll weevil. 



44 



INSECT ENEMIES OF THE BOLL WEEVIL. 



Pediculoides ventricosus Newport (fig. 8). This iiiite has been 
somewhat prominent in the study of the boll weevil since its first 
notice in 1901 (Rangel, 1901) under the name of Pediculoides ven- 



THE BOLL WEEV/L COMPLEX. 



THE COTTOA/ PLANT 

'NEM/ES 







AMONG MANyo. 

LE/IF 
WO> 



f2 

PREDA- 
TORS 
PREt)ATOPS 0/<^ARVAE 



HyPERPARAS/TE 



THESE /NUMEROUS E/\/EM/ES ALSl 
AREmOWA/ TO ATTACK AT LEAST. 



E2 

OTHER 
WEEI//LS 



3/ 

OTHER 
SPEC/ES 

OF 
PLANTS 



e 

HyPER- 
PARAS/TES 



Fui. G.— Diagram illustrating the boll- weevil complex. (Original.) 

triculosus. Mr. Banks has stated that it may possibly be different 
from the European species, but as it is known throughout tliis 
country imder the above name it is so quoted here. IMr. Rangel 



PARASITES OF WEEVIL AND OTHER HOSTS. 



45 



WEOTMER HOSTS 

^R/A B/S/e/VAT/i 
Lar/a COMPRESS/CORAJ/S 
IaRIA eXfGUA 

Lar/a obtecta 
Laria 0CHRAC£A 
Lar/a sallae/ \ 

SpERMOPMAGUS ROB/NMe 
BRACHyrARSC/S alternatus 
Araecerus pasciculatus 
l/xus musculus 
L/xus scPoa/coLus 
Smicronvx tvcho/des 
Desmor/s scapaus 
Ap/on decolopatum 
Ap/om grjseum 
Ap/om n/grum 
Ap/oa/ rostrum 
Ap/oa/ segwpes 
AIacrorhoptus sphaeralc/ae 
Tachypterellus quadric/bbos 
Smicraulax tuberculatus 

Afi/THOfJOMUS AEA/EOLUS 

Anthoa/omus albopilosus 
Anthoa/omus aphanosteph/ 
Anthoa/omus eugeaji/ 
Aa/thomoa^us pulvus 
Aa/thoa/oa/ius grand/s 
Aa/thoajoa^us heterothecae 
Aa/thoajomus ligatus 
Anthonomus nebulosus 
Anthonomus u/grinus 
Anthonoa^us s/gajatus 
Aa/THCNOA/!US squaa^osus 
TyCHIUS SORD/puS 
CONOTRACHELUS AFFJAJ/5 
CONOTRACHEWS ELEGANS 
CONOTRACHELUS JUGLANDIS 
CONOTRACHELUS fl/ASO 

conotrachelus a/ea/uphar 
Chalcodera^us aea/eus 

TyLODERMA POVGJLATUAa 

Gerstaecker/a a/obius 
auleutes tenu/pes 
Crapoaz/us /NAEQUAUS 
Ceutorhyajchus SP. 
Rhinoajcus PYRRROPUS 
Baris cuajeipeajaj/s 

BaRIS SP. 

Orthoris CRorcR/f 
Tr/crobar/s COMPACTA 
Trichobaris TEXAAJA 
Trichobaris trinotata 
Aa/ipeloglypter sesostris 
ZygodaR/s xantroxyu 
6alan/a/us a/as/cus 
Calandra oryza 
TOTAL A/OAJe£Tf OT HOSTS 







(4: S J m 



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Fig. 7.— Diagram giving the parasites of the boll weevil and their other hosts. (Original.) 



46 



INSECT ENEMIES OF THE BOLL, WEEVIL. 



pointed out that these mites reproduce viviparously and that their 
offspimg are mature and fertile at birth. He found that when they 
attach themselves to a host the abdomen commences to inflate 
until it becomes many times larger than the thorax. The time 
requii'ed for engorgement varies from 2 to 5 days. "VVlien the abdo- 
men commences to grow, the young commence to leave the parent. 
The males fertilize the females before leaving the parent's body and 
shortly afterwards die. An average of 100 female offspring to an 
individual was recorded. Rangel found that in 48 hours, 21 stages 
out of 40 in squares were attacked by the mites. In larger series of 
tests, after four days 50 out of 153 weevil stages in squares were 
attacked, or 32.6 per cent. 





a 

Fig. 8. — Pediculoidcs ventricosus: a, Adult female before inflation of abdomen with eggs and young; 
6, adult female after inflation of abdomen with eggs and young. Greatly enlarged. (Redrawn from 
Brucker.) 

Pediculoides n. sp. This mite was discovered in the laboratory at 
Dallas, Tex., June 13, 1907, by the senior author. Careful observa- 
tions on the length of generations were made with the following 
results: A gravid female was isolated June 13 and on June 17 there 
were 31 gravid mites. All but 5 were removed. On June 19 there 
were many offspring, one mite being well grown. On June 21 the 
fourth generation began to appear. In other words, between June 
13 and June 21, that is, in less than 8 days, there were two com- 
plete generations. Another genealogy was as follows : Parent isolated 
June 13, second generation began to appear June 14, were mature 



FLIES WHICH PARASITIZE THE WEEVIL. 47 

June 17, and reproducing June 19. On June 24 the third generation 
was reproducing. In this case there were 11 days covering two com- 
plete generations. 

The mites appeared wilhng to feed on any insect food available, 
as they were first found feeding on stages of Trichoharis compacta, 
then on boll-weevil stages, and finally on a Baris, on boll-weevil 
parasites isolated in rearing tubes, and on Hydnocera pubescens. 
They were reared readily on larvse of CMorion cyaneum and Polistes 
ruhiginosus. ]\ir. John B. Railsback, of Forbing, La., found that 
they attacked the larvae of the bollwonn and other smooth cater- 
pillars very readily. 

TYROGLYPHID.E. 

Tyroglyphus hreviceps Banks was described as a weevil enemy 
from Victoria, Tex. This, or a similar mite, was found to be very- 
abundant at Calvert, Tex., in 1906. 

4. FLIES WHICH PARASITIZE THE BOLL WEEVIL. 

Veiy few Diptera are laiown to be primarily parasitic upon boll 
weevils, but the genera Myiophasia and Ennyomma in the Tacliinidse 
seem to be confined to hosts of this nature. The genus Aphiochseta, 
of the Phoridse, contams at least 3 species which have been reared 
under circumstances pointing to primaiy parasitism. The larvae of 
the tachinids work singly and those of Apliiochseta several to a host, 
but in both cases as endoparasites. Wlaen the former become full 
grown they completely fill the sldns of the weevil larva3 and fre- 
quently the appendages of Myiophasia penetrate to the exterior. 
The weevil skin partakes of the character of parchment and becomes 
a cocoon witliin wliich the fly larva pupates and fi'om wliich the 
adult emerges. On the contrary the Apliiochseta larvae leave the 
host when they have reduced it to a shell and pupate in the weevil 
cell. 

The flies evidently prefer to attack weevil stages in moist, shaded 
spots in preference to sunny locations. By tliis habit they become 
very valuable in fields located in bottom lands where the diy condi- 
tions conducive to parasites like the hymenopterous parasites are 
absent. The puparia of Myiophasia and Ennyomma are so near 
like that of the chalcidoid internal parasite Tetrastichus hunteri that 
they can be differentiated only by the larger size of the dipterous 
puparia. 

PHORID.E. 

ApMochseta nigriceps Loew (determined by D. W. Coquillett) . 
Apliiochseta fasciata Fallen (determined by D. W. Coquillett). 
ApMochseta pygmsea Zetterstedt (determined by D. W. Coquillett) . 



48 INSECT ENEMIES OP THE BOLL WEEVIL. 

On September 12, 1906, in dry hanging bolls collected at Dallas, 
Tex., a weevil larva was found parasitized and isolated in a separate 
tube, with the following record: "Veiy small parasite larva on small 
weevil larva." On September 26 a single specimen of Apliiochsnta 
nigriccps Loew was reared and the following note made by the 
senior author: '* Found dipterous puparium, skin of liaiiy para- 
site larva (may be the dipteron or a hymenoptcron) ; also remains 
of weevil larva." On October 6, 1906, in hanging bolls collected 
at Dallas a weevil larva was isolated with the note, "Weevil larva 
full of dipterous larvae." Eleven larvte left this host larva and 
pupated. On October 29, 7 Aphiocliseta {Vj fasciata Fallen and two 
A. pygmsea Zetterstedt were reared. At least the latter case seems to 
be very strong evidence of primary parasitism. These flies are reared 
frequently from bolls and many are perhaps scavengers. Two other 
species, A. epeirse Brues and A. scalaris Loew, have also been reared 
from cotton forms at Calvert, Tex. Kecords made in 1911, at Tal- 
iulah, La., by Mr. Harry Pinkus, point conclusively to primary 
parasitism. 

TACHINID^. 

Myiophasia senea Wiedemann is recorded from a number of very 
important weevils. Of these, Balaninus nasicus Say (the acorn 
weevil), Conotrachelus juglmidis LeConte(the walnut weevil), ^/n;pe- 
loglypter sesostris LeConte (the grapevine gall-maker), Conotrachelus 
affinis Boheman (the hickory-nut weevil), and Conotrachelus elegans 
Say (the pecan-gall weevil) are all weevils which enter the ground for 
pupation, carrying their parasites with them, and consequently it 
becomes necessary for the flies to emerge from the weevil cell through 
several inches of earth before attaining freedom. The only weevils 
which this fly attacks and which do not enter the ground for pupation 
are the boll weevil and Triclioharis compacta Casey (the Jamestown- 
weed pod weevil). Very few records have been made to ascertain 
its developmental period, but the three records at hand indicate from 
22 to 29 days as the period from collection of the infested material 
to the maturity of the fly. This period would cover largely the under- 
ground period only. 

Ennyomma (Loewia) glohosa Townsend. Several specimens of 
this fly were reared during 1907 by Mr. C. R. Jones at Alexandria, 
La., as primary parasites of the boll weevil. It is a very common 
parasite of Chalcodermus seneus Boheman (the cowpea-pod weevil) 
in the Southern States. 

5. THE HYMENOPTEROUS PARASITES OF THE BOLL WEEVIL. 

So much information has been gained concerning the hymenopter- 
ous parasites of the boll weevil that it will be necessary to omit 
manj^ of the technical facts learned about them. The present sec- 



HYMENOPTEEOUS PARASITES OF THE WEEVIL. 



49 



tion is concerned with the sources of the parasites and with important 
records of their occurrence, whUe the other interesting facts to be 
presented are inchided in the five following sections : 

CHALCIDOIDEA. CHALCIDID.E. CHALCIDIN^. SMICRINI. 

Spilochalcis sp. A single male of this species was found dead in a 
weevil ceil with the remains of the weevil and its own exuvium in a 
hanging square collected August 10, 1907, at Victoria, Tex. 

TORYMID.E. MONODONTOMERIN.E. 

Microdontomerus anthonomi Crawford (fig. 9). Brachytarsus alter- 
natus Say was formerly the only weevil recorded as a host of this 
species. A male and female of this parasite were reared on Septem- 




'EiG.'i.— Microdontomerus anthonomi: Adult. Much enlarged. (Origiual.) 

ber 12, 1907, from pods of the flowering shrub Amorpha fruticosa, at 
Dallas, Tex., which were highly infested by (Bruchus) Laria exigua 
Horn. In 1906, in which year this parasite was first discovered, it 
ranked as seventh species in importance as a boll-weevil enemy. 
In 1907 it advanced to fourth place and was very important in the 
central black-prairie region of Texas. In 1909 the easternmost 
limit of our records was Tallulah, La., which did not become infested 
by the boll weevil until 1908. 

EURYTOMID.'E. EURYTOMINI. 

Euryfoma tylodermatis Ashmead {BruchopTiagus Tierrerse Ashmead). 
This is without doubt one of the most important species under 
consideration, having a range of distribution practically coexten- 
16844°— Bull. 100—12 4 



50 INSECT ENEMIES OF THE BOLL WEEVIL. 

sive with that of its host, the boll weevil. In previous publi- 
cations it has been recorded as a parasite of Lixus musculus Say, L. 
scrohicollis Boheman, Apion segnipes Say, Anthonomus JieterothecsR 
Pierce, Anthonomus squamosus LeConte, Tyloderma foveolatum Say, 
and Orthoris crotchii LeConte. To this list may be added (Bruchus) 
Laria exigua Horn in Amorpha pods at Dallas, Tex.; (Bruchus) 
Laria sallxi Sharp in pods of huisache ( VaclieMa farnesiana) col- 
lected at Victoria, Tex.; Spermopliagus rohinise Schonherr in pods of 
the honey and water locusts ( Gleditsia triacanthos and G. aquatica) 
in Louisiana; Macrorhoptus sphxralcise. Pierce in pods of Sphseralcia 
at Del Rio, Tex.; Smicraulax tuherculatus Pierce in mistletoe stems 
at Dallas, Tex.; TricJwharis texana LeConte in stems of Solanum 
rostratum at Cisco and Victoria, Tex.; and also Triclioharis trinotata 
Say; and finally it was reared in September, 1908, from Baris sp. in 
roots of ambrosia at Camden, Ark., by C. E. Hood. 

Euryfoma sp. A female primary parasite and a male accidentally 
secondary on Microhracon mellitor Say were reared from hanging 
squares collected August 10, 1907, at Victoria, Tex. 

PERILAMPID.E. 

Perilampus sp. A single individual was reared from the boll weevil 
iji an isolated weevil cell by C. E. Hood from squares collected Sep- 
tember 7, 1907, at Shreveport, La. Another specimen of Perilampus 
was reared from squares collected at Granbury, Tex., August 8, 1907, 
but its source could not be proved. If it were not for the definite 
record made by Mr. Hood these species could hardly be placed in 
this list. This record may possibly be based upon the parasite of an 
intruder in the weevil cell instead of upon the weevil itself. It is 
not impossible that after several years this parasite may be found 
normally as a boll-weevil parasite, as was the case with Sigalphus 
curculionis. 

ENCYRTID^. EUPELMIN^. 

Cerambycohius cyaniceps Ashmead. The list of hosts of this spe- 
cies as previously recorded included Anthonomus alhopilosus Dietz, 
{Bruchus) Laria ohtecta Say, L. exigua Horn, Lixus musculus Say, 
Tricholaris texana LeConte, and Tyloderma foveolatum Say. To this 
list may be added Laria hisignata Horn in pods of Acuan illinoensis; 
L. ochracea Schaeffer in pods of Vicia sp.; L. sallxi Sharp in pods of 
huisache ( Vachellia farnesiana) ; Spermophagus rohinise Schonherr in 
pods of Gleditsia triacanthos at Alexandria, La.; Lixus scrohicollis 
Boheman in stems of Ambrosia trifida and A. psilostaclmja; Apion 
rostrum Say in pods of Baptisia tinctoria at Washington, D. C; 
Tachypterellus quadrigibhus Say in fruit of Cratsegus mollis at Vic- 
toria, Tex.; Smicraulax tuherculatus Pierce in stems of mistletoe 



HYMENOPTEEOUS PARASITES OF THE WEEVIL. 51 

(PJioradendron flavescens) ; Tychius sordidus LeConte in Baptisia 
pods at College Station, Tex.; Trichoharis compada Casey in pods of 
Datura stramonium at Paris, Tex.; and, furthermore, on Langurla 
sp. in stems of Gaura sp. at Ballinger, Tex. 

Ceramhjcohius cushmani Crawford. This parasite was reared in 
small numbers as early as 1906 in southern Texas from the boll 
weevil. It has been reared from Laria ochracea Schaeffer in pods of 
Vicia sp.; from L. sallsei Sharp in pods of VaclieUiafarnesiana; from 
Arsecerus fasciculaius DeGeer in fruit of chinaberries ( Melia azeda- 
racli) at Victoria, Tex.; and from Trichoharis texana in stems of 
Solarium, rostratum . 

Oeramhycohius sp. On February 23, 1909, a male of a green species 
of Cerambycobius was reared from the weevil in squares collected at 
Natchez, Miss., January 19. 

PTEROMALID.E. PTEROMALIN^. 

Catolaccus hunteri Crawford. This is the species which in all pre- 
vious articles on the boll weevil has been known as Catolaccus incertus. 
Its hosts as now known are Laria compressicornis Schaeffer in pods of 
Acuan illinoensis; Tachy pterellus quadrigihhus Say in fruit of Cratsegus 
spp. ; Smicraulax tuherculatus Pierce in stems of Plioradendron flaves- 
cens; Anthonomus seneolus Dietz in buds of Solanum spp. ; Anthono- 
mus alhopilosus Dietz in seeds of Croton sp.; Anthonomus eugenii 
Cano in fruit of pepper {Capsicum spp.); Anthonomus heterothecx 
Pierce in heads of Heterotheca ' subaxillaris; Anthonomus nebulosus 
LeConte in buds of Cratxgus spp.; Anthonomus signatus Say in buds 
of dewberry (Ruhus spp.) ; Anthonomus squamosus Le Conte in heads 
of Grindelia squarrosa nuda; {Acalles) GerstsecTceria nohilis Le Conte in 
joints of Opuntia spp. ; Zygoharis xanthoxyli Pierce in berries of Xan- 
thoxylum clava-herculis. 

Catolaccus incertus Ashmead. This parasite is also very common 
and is known from a considerable number of hosts, among which are 
Laria exigua Le Conte in pods of Amorpha fruticosa; Apion decolora- 
tum Smith in pods of Meihomia paniculata; Apion griseum Smith in 
pods of Phaseolus spp. ; Apion nigrum Smith in buds of Rohinia pseu- 
dacacia; Anthonomus alhopilosus Dietz in seeds of Croton spp. ; Antho- 
nomus aphanostephi Pierce in heads of Aphanostephus sMrrohasis ; 
Anthojiomus fulvus Le Conte in buds of Callirrhoe involucrata; Antho- 
nomus nigrinus Boheman in buds of Solanum carolinense; Anthonomus 
signatus Say in buds of strawberry (Fragaria virginiana); Auleutes 
tenuipes Dietz in buds of Galpinsia hartwegi; Ceutorhynclmis n. sp. in 
crown of Selenia aurea; Baris cuneipennis Casey in roots of Helenium 
tenuifolium and Calandra oryza Linnaeus in corii 



52 



INSECT ENEMIES OF THE BOLL WEEVIL. 



Hahrocijfus lyiercei Crawford, This is a brilliant green parasite 
resembling Catolaccus antJionomi Ashmead. It is reared from the boll 
weevil mamly in the fall and from hibernated inuividuals in the spring. 
It has been reared from Laria compressicornis Schaeffer in pods of 
Acuan illinoensis. (See fig. 10.) 

Lariophagus texanus Crawford. There is every evidence that this 
species is a true parasite of the boll weevil, although it has not been 
positively reared by isolation from the boll weevil. On August 17 
and 27, 1907, two specimens were reared from material collected at 
Hallettsville, Tex., August 13; on August 19 and 23 three specimens 
were reared from cotton squares collected at Victoria, Tex. ; on August 
29 three specimens were reared from squares which were collected at 
Eagle Lake, Tex., on August 14. The Victoria lot was pecuUar in that 
it furnished the first records of Cermribycohius cushmani Crawford, 
Spilochalcis sp., and Eurytoma n. sp. This species is described as a 
parasite of (Bruchus) Laria prosopis Le Conte. It 
undoubtedly also attacks L. sallsei Sharp, which 
also breeds in the pods of huisache; furthermore, 
the species was reared from stem galls of Leucosyris 
spinosus containing Anthonomus ligatus Dietz. 

Tetrasticlms hunteri Crawford. This interesting 
new parasite of the boll weevil was first reared in 
the fall of 1908 from isolated parasitized individuals 
of the boll weevil collected at Natchez, Miss., by 
H. S. Smith. It is internal in weevil larvae and 
pupae and has even been reared from immature 
adults. A parasitized individual can easily be told 
by its brownish color and smoothening of the vari- 
ous segmental wrinkles. In more advanced stages 
of the parasite's development, the parasitized in- 
dividual becomes a mere bro"\vn skin of parchment. Tliis skin serves 
as puparium for the parasite. The developmental period is of con- 
siderable length in the fall. Specimens isolated in November do 
not mature until April or May. In 1908 it was found only at Natchez, 
IVIiss., and Monroe, La., but in 1909 it was reared at a number of places 
in Louisiana and also at Arlington, Tex. This species gives an ex- 
cellent example of the adjustment of native parasites to the boll 
weevil. 

ICHNEUMONOIDEA. ICHNEUMONID.E. PIMPLIN.i;. 




Fig. IQ.—Habrocytus 
piercei: Pupa. Much 
enlarged. (Original.) 



Pimpla sp. On January 27, 1909, a larva of this species was 
isolated from a weevil larva in squares collected at Nacogdoches, Tex. 
This became a mature female on February 23. 



HYMENOPTEEOUS PARASITES OP THE WEE\^I. 



53 



BRACONID^. SIGALPHIN^. 



Sigalplius curculionis Fitch. Previous to the summer of 1908 the 
first record of rearing this species (see fig. 11) from the boll weevil was 
considered doubtful, but beginning in August it was reared repeatedly 
in material from Ruston and Monroe, La., and Natchez, Miss. Its 
other hosts are Conotrachelus afjinls Boheman in hickory nuts; Cono- 
trachelus elegans Boheman in petioles of hickory at Dallas, Tex., and 
in galls of Phylloxera devasfatrix on pecan {Hicorla pecan) at Dallas 
and Victoria, Tex. ; Conotraclielus juglandis Le Conte in walnuts (Jug- 
lans nigra); Conotraclielus nenuphar Herbst in fruit of plum, peach, 
etc.; Tyloderma foveolatum Say in stems of Onagra biennis at Wash- 
ington, D.C. ; Trichoharis texana Le Conte in stems of Solanum rostra- 
turn; Trichoharis trinotata 
Say in stems of potato (Sol- 
anum, tuherosu'in) ; and Zygo- 
haris xantJioxyli Pierce in 
seed of Xanthoxylum clava- 
herculis. 

Urosigalphus anthonomi 
Crawford has never been 
reared since the original 
records which were made 
at Brownsville, Tex. 

Urosigalphus schwarzi 
Crawford. This Guatemalan boll weevil parasite has never been 
reared in the United States. 

Urosigalphus n. sp. At Arlington, Tex., in 1909, a single specimen 
was reared from an isolated cocoon. 




Fig. 11. — Sigalphus curculionis: a, Male; h, female; c, an- 
tenna. All enlarged. (After Riley.) 



BEACONING. 

Microhracon mellitor Say.^ This parasite (see fig. 12) still holds 
the lead as the most important boll-weevil parasite. Its other 
host relations are only partially discovered. The following hosts 
have been ascertained: Desmoris scapalis Le Conte in heads 
of Siderantlius ruhiginosus; Smicraulax tuberculatus Pierce in 
stems of Phoradendron Jiavescens; Anthonomus alhopilosus Dietz in 
seed of Croton spp.; Anthonomus eugenii Cano in fruit of pepper 

1 Bracon mellitor Say is recorded by Giranlt (1907) as a parasite of the lesser peach borer {Synanthedon pic- 
tipes Oroto and Robinson) and of tiie peach borer (Sanninoidea exUiosa Say). The gregarious habit of these 
parasites appears to prove that the determination was incorrect. Mr. F. E. Brooks, of West Virginia, has fur- 
nished the record of this species from Sanninoidea exitiosa and also from Craponius inxqualis Say at French 
Creek, W. Va. The determinations were made in the Bureau of Entomology. Dr. F. H. Chittenden states 
that he reared this species from the strawberry leaf-roller, A ncylis comptana Froelich (fragarix Walsh and 
Riley), at Cabin John, Md., July 9, 1899. It is probable that all parasites of Lepidoptcra determined as 
Bracon mellitor belong to some other species. The lepi-dopterous and coleopterous parasites are not dis- 
tinguishable by structural characters, but are so different in habits that it is considered advisable to 
call the lepidopterous parasite Microbracon dorttator Say aud the coleopterous parasite M. mellitor Say. 



54 



INSECT ENEMIES OF THE BOLL WEEVIL. 



(Capsicum sYip.); Anthonomus fulvus Le Conte in buds of CalUrrhoe 
involucrato; Antlionomus squamosus Le Conte in heads of GriTuLelia 
squarrosa nuda; Conotrachelus nenwphar Herbst in peaches ; Tyloderma 
foveolafum Say in stems of Onmjra hiennis; Cra/ponius inxqualis Say in 
fruit of grape ( Vitis spp.), and Barls sp. in roots of Ambrosia sp. 

0. BIOLOGICAL NOTES UPON THE PARASITES OF THE WEEVIL. 

A number of very interesting facts, wliich deserve mention in an 
economic bulletin, have been learned about the biology of the parasites. 

ABUNDANCE OF PARASITES. 

It is unusual for the parasites of the boll weevil to be found flying 
in numbers. Their work is in a general way quietly and unostenta- 
tiously done, but occasionally it is the pri\dlege of the observers to 
see swarms of parasites hovering around the food plant of their 

favorite host. At Clar- 
endon, Tex., in August 
and September, 1905, Mr. 
C. R. Jones and the sen- 
ior author witnessed large 
numbers of Microhracon 
nuperus and Tetrasticlius 
sp. hovering around the 
highly infested pods of 
Mentzelia nuda. The par- 
asitism in pods gathered 
at this time was so high 
that much superparasit- 
ism by Tetrasticlius upon 
theMicrobracon occurred. 
At Ruston, La., in Octo- 
ber, 1907, the senior 
author saw Catolaccus 
hunteri flying in all directions and resting on the flowers and 
leaves of Heterotlieca suhaxillaris and found a very high parasitism 
of Anthonomus heterothecse. by this species. In November, 1908, 
in this same field at Huston, a very high percentage of parasitism 
of the boll weevil by Catolaccus was found. In September, 1908, 
Mr. Hood saw many species of parasites around the flower heads 
of Vernonia at Camden, Ai-k. During the same month Mr. H. S. 
Smith found Catolaccus hunteri swarming on Croton capitatus contain- 
ing Anthonomus albopilosus. Such observations are very important 
because they suggest excellent sources for parasites to be used in 
introduction experiments or suggest forcing of the parasites to the 
boll weevil by the elimination of the host. 




Fig. 12.- 



■ Microbracon mellitor: Adalt. Mucheolarged. (From 
HiintPi-and Hinds.) 



BIOLOGICAL NOTES ON THE PARASITES. 55 

FREQUENTATION OF NECTARIES. 

The feeding habits of adult hymenopterous parasites have long 
escaped observation, but witliin recent years the intensive study of 
parasites has proved that very little can be accomplished in the prop- 
agation of parasites unless they can be fed. In the case of the para- 
sites of the boll weevil it is impossible for the adults to obtain nour- 
ishment from the host in which they are ovipositing, as has been 
proven in the case of parasites of externally feeding insects. The 
host plant of the boll weevil, however, furnishes the desired food. 
The nectaries of cotton are about as plentiful as those of any other 
plant. The majority of varieties of cotton have three large nectaries 
on the leaves and also have them on the outside and inside of the 
involucre, as well as on the inside of the flower. Frequent observa- 
tions of cotton plants wliich were producing considerable nectar have 
enabled us to observe practically all of the parasites of the boll 
weevil, as well as all of the ant enemies and many other insects. 
Some of these insects wliich visit the nectaries are injurious to the 
cotton plant, but the majority seem to be beneficial. 

The quantity of nectar secreted by various varieties of cotton is 
quite variable. The variety which seems to secrete more than any 
other which has been observed is the Egyptian Alit Afifi. Tliis variety 
is frequently surrounded by large numbers of beneficial hymenop- 
terous insects, although at the same time it appears to be very sus- 
ceptible to boll weevil attack. 

HELIOTROPISM. 

The majority of the hymenopterous insects wliich have been under 
observation in tliis investigation appear to be positively heliotropic. 
In general this tendency can be utilized in rearing-cage technique to 
induce the parasites to go into small tubes placed in the rearing boxes, 
from which they can be easily removed. It has been noticed in 
rearing cages in wliich there were growdng plants with plenty of food, 
air, and heat, that the parasites sought the lightest portion of the 
cage rather than the plants wliich could give them some shade from 
the hot sun. 

The activity of the parasites is greatest when the sunlight is most 
intense. Observations at the nectaries of the Eg3^ptian cotton con- 
firmed this. Wlien the sun was shining the parasites were very 
active at the nectaries and flying around the plants, but when a 
cloud passed over they seemed to disappear entirely. On cloudy 
days none of the Hymenoptera, except the most industrious bees and 
wasps, was to be found at the nectar. Trelease (1879) states that 
"the extrafloral nectar of the cotton plant is far more abundant 
during night and in the early morning than at any other time, and 



56 



INSECT ENEMIES OF THE BOLL WEEVIL. 



this is true whether we consider the invokicral or fohar glands," The 
parasites probably frequent the nectaries during the morning sunlight 
hours and then are equipped to go about their other duties during the 
hottest part of the day. 

In addition to these actual observations as to the preference of 
parasites there are other very strong proofs of heliotropism. It has 
been found that there is a decided increase in the parasitism of weevil 
stages in hanging forms exposed to the sun over those in fallen forms 
which are more or less shaded. It is also apparent that the fallen 
forms most exposed to the sun receive the greater amount of para- 
sitism. Among the hymenopterous parasites there is only one at 
present which seems to prefer a moist shady place for its work. 
This is Tetrastichus liunteri C^rawford, which is an internal parasite. 



A numerical study of the records of rearing of parasites from the 
boll weevil shows that in the majority of the species the males are 
relatively fewer than the females. The following table will show the 
percentage of each sex and also the number of parasites upon which 
these percentages are based. 

Table XIX. — Relative percentages of the sexes of boll-iveevil parasites. 



Species. 



Total in- 
dividuals. 



Percentage of sexes. 



Female. Male 



Microbracon meUitor 

Catolaccus liunteri 

Catolaccus incertus 

Habrocytus piereei 

Cerambycobius cushmani 

Cerambycobius cyaniceps 

Cerambycobius sp 

Ennyomma globosa 

Etirytoma tyloderniatis 

Eur'ytoma sp 

Lariophagus texanus 

Microdontornerus antUonomi 

Myiophasia xnea 

Sigalphus curculionis 

Tetrastichus liunteri 



429 

30 

64 

509 

1 

8 

433 

2 

2 

223 

2 

13 

41 



Per cent. 
GO. 78 
78.37 
81.12 

100.00 
71.88 
70.34 

37.50 
64.90 
50.00 
50.00 
84.76 
50.00 
61. 54 

100.00 



Per cent. 
39.22 
21.63 
18.88 



28.12 
29.66 
100.00 
62.50 
35.10 
50.00 
50.00 
1.5.24 
50.00 
38.46 



OVIPOSITION. 



It has been found by numerical study of the large number of para- 
sites collected during the last five years that whenever the parasitism 
in a field reaches between 50 and 70 per cent there is a strong likeli- 
hood of reduplication, with resulting superparasitism. The exact 
records of superparasitism obtained in this investigation have been 
published in another article (Pierce, 1910). Parasites have no power 
of discerning the presence of another egg on the prospective hosts, 
and hence there occurs at times a tremendous duplication of energies. 



Bui. 100, Buieau of Entomo'ogy, U, S. Dept. of Agriculture 



Plate II. 







Eggs of Boll-Weevil Parasites. 

Fig. 1.— Type II. Micnidontom, rm anthononii; Calvert. Tex., Augu.Mt 23, 1907; color white; 
size 0.38 by 11 mm. Fig. 2.— Type VI. Unidentified egg: Dallas, Te.x., November 11, 
1907. color white; size 0..S5 by 0.19 mm. Fig. 3.— Type I. Crraiiibi/rdbim ei/nniccps; Sa, view 
from side: Sh. view from end: color white: size about O.S mm. ' Fig. 4.— Tvpe III. Eiiri/- 
Idiiiati/todentiatis: Dallas, Tex.. August 22, 1907: color gray; size O.tlS bv 0.21 mm.; !,a, side 
view of another egg. Fig. 5.— Type IV. CutolaccuK hiinteri; Dallas, Tex,, August 22, 1907; 
cctlor white: size 0.(i2 by 0,22 mm. Fig. 6.— Type V, Unidentified egg; Glenmora, La., 
August 2;i. 1907; color grav: size 0.44 bv 0.11 mm. (Original. ) 



Bui. 100, Bureau of Entomoiogy, U, S. Dept. of Agriculture, 



Plate III, 









Parasites of Weevils. 

Fig. \.—E>iriitoma tuloflrrmatix. pui.ii. Via. ■l. — Catolfunis incaiuf, pupca. _Fig_. S.—Crram- 
bvcnbiiis rii,u!irrij:<. pupa. Fig. i.—Micn>il<„itown;i>f arithonomi. pupa. Fig. o.-Larya ol 
microbracon. Fig. e.-MtcmbramnweUUor.vupsi. Fig. 7.-Larvaotchalcidoid. Mucli 
enlarged. (From Pierce.) 



DEVELOPMENT OF THE PARASITES. 57 

It may therefore be possible that a parasite will visit the same square 
several times and oviposit. In general it may be said that as the 
primary parasitism of the boll weevil increases the superparasitism 
also increases, with the result that sometimes the parasitism might 
be considerably increased if every egg reached a single host. The 
following instances will illustrate this. At Calvert, Tex., 41 stages 
were attacked by 44 parasites, although only 3G.5 per cent of the 
weevils were parasitized. If every parasite egg had reached a host, 
there would have been 107.3 per cent parasitism. At Dallas, Tex., 
out of 309 weevil stages, 44.6 per cent were attacked by 216 parasites. 
The possible parasitism was 69.9 per cent. Many other instances of 
this kind could be given, but these two cases illustrate the condition 
perfectly as it exists in many places during the fall of each year. 

The time for oviposition apparently differs for the various species. 
Microhracon mellitor, as a rule, oviposits before the boll-weevil larva 
has constructed a cell, that is, several days before the flared square falls 
or dries. Eurytoma tylodermatis appears to oviposit in squares on the 
plant after the normal time of falling and hence is more important in 
hanging dry sc^uares. Catolaccus spp. and Microdontomerus antlio- 
nomi favor fallen forms for oviposition. The chalcids generally 
oviposit after the weevil larva has formed its cell. Tetrastichus 
hunteri is most frequently found in fallen squares. 

7. THE DEVELOPMENT OF THE PARASITES, 

THE EGGS. 

The eggs of the boll-weevil parasites are all oblong-elliptic and 
either smooth or sculptured. The eggs of several species have at 
one or both ends a small tube which is tied into a knot. SLx tyiws of 
eggs of the boll-weevil parasites have been closely observed and 
designated by number in the records of rearing. These are illus- 
trated on Plate II. The eggs of all the boll-weevil parasites are 
placed in the weevil cell or on the larva or pupa and usually wdthout 
injuring the latter. 

Type I. — Type I is the egg of Ceramhycohius cyaniceps. It was 
determined for the species by the use of a mica plant cage in which 
the parasite was isolated with newly infested squares. This egg is 
about 0.8 mm. long, pure white, cylindrical, unsculptured, and with 
a narrow neck, which is twisted into a knot, probably by the ovi- 
positor after the latter has released it. (Plate II, fig. 3.) 

Type II. — This is the egg of Microdontomerus anthonomi, as shown 
by the rearing of an isolated specimen. The color is white, the egg 
being distinguished by the slightly papillose sculpture and by the 
nipple at one end. It measures 0.38 mm. in length and 0.11 mm. in 
breadth. (Plate II, fig. 1.) 



58 INSECT ENEMIES OP THE BOLL WEEVIL. 

Type in. — This is the egg of Eurytoma tylodermatis , found by the 
isoLation of a larva seen in the act of hatching, coUected at Dahas, 
Tex., August 22. The egg is dark-gray and thickly covered with 
spines. It measures 0.68 mm. in length and 0.21 mm. in breadth. 
The process at one end is frequently twisted. (Plate II, fig, 4.) 

Type IV. — This egg was practically identified as that of a Cato- 
laccus by isolation of specimens collected August 22 at Dallas, Tex. 
The color is white and the egg is covered with very small tubercles or 
papillge. It is 0.62 mm. long and 0.22 mm. broad. (Plate II, fig. 5.) 

Type V. — Tliis egg was taken only at Glenmora, La., August 23, 
on two weevil stages, and has not been identified. It is dark-gray 
and very spiny, but the spines are larger, longer, and sparser than in 
Type III. The length is 0.44 mm. and the breadth 0.19 mm. (Plate 
II, fig. 6.) 

Type VI. — This new type was discovered November 14 at Dallas, 
Tex., and has not yet been identified. There is no sculpturing what- 
ever. It is pure white. The length is 0.85 mm. and the breadth 
0.19 mm. (Plate II, fig. 2.) 

THE LAEV^. 

The larvae of the boll-weevil parasites live as readily on dead food 
as on fresh food. The hosts generally die within a very short time 
after the larvse begin attack. The larvae have been found pretty 
well grown with dry weevil larvae as food. They have been found 
on weevil larvae and pupae indiscriminately and several times under 
the elytra of teneral or unemerged adults. Just before transforming 
from the larva to pupa there is considerable meconial discharge. 
The majority of the boll-weevil parasites are external feeders, but 
the larvae of Myiophasia senea, Ennyomma glohosa, and Tetrastichus 
Jiunteri are internal feeders. These larvae kill the host in a short 
time, its skin becoming shriveled and forming a perfect puparium 
for the parasite. Pupation takes place within this skin. (PI. Ill, 
figs. 5, 7.) 

Pupation. — All the chalcidoid parasites have naked pupae. The 
braconids usually form silken cocoons of characteristic size, shape, 
mesh, or color. The cocoons of Microhracon mellitor are very vari- 
able in size, color, and consistency, so that they appear almost to 
belong to different insects. The cocoons of Sigalplius curculionis are 
generally of a rather bright yellow and with very fine silk. The 
pupal exuvium of the various species of chalcids and braconids is 
sufficiently characteristic to enable a skilled observer to determine 
the species after the parasite has left. (PL III, figs. 1-4, 6.) 

Rapidity of development. — It is rather difficult to make an accurate 
study of the developmental period of parasites, especially when every 
adult parasite that matures under observation must be saved, if 



DEVELOPMENT OF THE PARASITES. 59 

possible, for further experimentation or for determination. It is 
inadvisable to isolate many of the parasites until the larva is partially 
developed, as the isolation seems to dry out both food and larva. 
In the study of the parasites all those in the same stage were placed 
on the same tray. Wlien they passed to the next stage in develop- 
ment they were transferred to another tray. In this manner an accu- 
rate record was kept of the development. In order to determine the 
total length of the breeding period it seems best to take the total 
period from the collection of the material to the maturity of the last 
specimen and add a plus mark ( + ) to this figure. The total period 
can hardly be more than 2 or 3 days longer than the longest period 
thus obtained, as the egg period is very seldom more than 3 days. 
To obtain the exact length of the pupal period, the maxinnim period 
is taken to be the longest time from the observation of a fresh or 
newly-formed pupa to maturity, and the minimum time is taken to be 
the shortest period from the observation of the grown larva to ma- 
turity. Having thus accurately defined the pupal stage, the relative 
limits of the egg and larval stages are obtained by subtracting 
the pupal stage from the total developmental period. Table XX, 
which follows, presents all of the available data as they have been 
reduced in this manner to show the length of development of the 
various stages. It will be seen that most of the species ])ass their 
entire developmental period in from 20 to 30 days between June and 
October 15, but that after the middle of October the developing 
stages are caught by the cold weather and the development is sus- 
pended until spring. Thus, it is noticeable that parasites becoming 
larvae in early October and November have a short larval period of 
probably less than 20 days, becoming pupae before the cold wave 
and passing a pupal period of about 150 days. Parasite larvae 
which hatch a little later are caught in the larval stage and hibernate 
thus for from 120 to 150 days, then becoming pupa? and maturing 
in from 15 to 40 days. It will be noticed that Microbracon mellito?', 
Eurytoma tylodermatis, and the two species of Catolaccus have short 
developmental periods during the summer, while the species of 
Cerambycobius have a little longer period. It will be noticed that 
Hahrocytus inercSi has only appeared in the fall of the year. This 
species has been recorded four years in succession and never before 
October. On the other hand, Microdontomcrus anthonomi seems to 
be almost exclusively a summer parasite, having never been recorded 
after September. Of course the species of which we have records 
throughout the breeding season are the ones most important. This 
statement is borne out by the figures on the relative numbers and 
importance of the dift'erent species. 



60 INSECT ENEMIES OF THE BOLL WEEVIL. 

Table XX. — Lengths of developmental periods of the holl-weevil parasites. 



Species and period. 


June. 


July. 


August 


Sep- 
tember 


Octobei 
1-15. 


■ October 
15-30. 


Novem- 
ber. 


Decem- 
ber. 


Microhracon mcllitor: 

Egg and larva 


Days. 
13-19 

2-8 
21 + 


Days. 

0-8 
5-7 
13+ 


Days. 
10-15 
3-8 

18+ 


Days. 
0-10 

4-8 
14+ 


Days. 
6-20 
10-26 
30+ 

20+ 
14+ 
34+ 

8-25+ 
8-22 
10-33+ 

20-40 

13 

33-53 


Days. 

9+ 
141-147 
150+ 


Days. 


Days. 

118+ 

14+ 

132+ 

70+ 
15 + 
85 + 

70+ 


Pupa 




Total 


156+ 

21 + 
13+ 
34-138+ 


Hahrocytus piercei: 

Egg and larva 


Pupa 












Total 












Calolaceus hunteri: 

Egg and larva 


9-14+ 
0-11 

20+ 

9-10+ 

7-8 
17+ 


14-17+ 

4-7 
21 + 

9-12+ 
0-9 
18+ 


9-12+ 
5-7 
16-17 

5-11 + 
0-8 
13-15 


13-15 

6-8 
21 + 

9-12+ 
6-9 

18+ 




Pupa 




7-12 
16+ 


15+ 
85+ 


Total 




Catolaccus incertus: 

Egg and larva 






Pupa.. 








Total 




67+ 




Cerambycobius sp. : 

Egg and larva 




65+ 


Pupa 
















18+ 


Total 
















83+ 


Cerambycobius cushmani: 

Egg and larva 




13+ 
3 + 
16+ 

6-9 
10-13 
19+ 

11-10+ 
4-9 

20+ 

4-10+ 
6-12 
16+ 


16+ 
-12 

28+ 

15-19 
7-11 

26+ 


7-11 + 
7-11 
18+ 

16-20 
8-12 
28+ 








Pupa 












Total 












Cerambycobius cyaniceps: 

Egg and larva 


10+ 
9+ 
19+ 


18+ 

7+ 

25+ 






84-113 


Pupa 






19-37 


Total 


129+ 


139+ 


191 150 


Ennyomma globosa: 

Egg and larva 




Pupa 
















Total 
















Eurytoma tylodermatis: 

Egg and larva 


11-12+ 
5-6 
17+ 


12-25+ 
5-9 
21-30 

15+ 

11-36 
5-6 
17-41 

8+ 
8-11 
10+ 


8-9 
7-8 
16+ 


11+ 
15-23 

26+ 


158+ 
20+ 
178+ 




110+ 


Pupa 




17 25 


Total 




135+ 


Lariophagus tezanus 






Microdontor.icrKS an/honomi: 
Egg and larva 




14-15 

6-7 
21+ 


26 + 

6-11 
32-37 










Pupa 












Total 


20+ 










Myiophasia xnca: 

Egg and larva 










Pupa 
















Total 
















Pimpto sp.: 

Egg and larva 














62+ 


Pupa 
















15- 


Total 
















87+ 


SigalpTius curculionis: 

Egg and larva 










17-20+ 

13-16 

33+ 








Pupa 
















Total 
















Tctrastichus hunteri: 

Egg and larva 




8-11+ 
16-19 

27+ 






143-216+ 
31+ 
174-216+ 






Pupa 














Total 














Urosigalphus anthonomi: 

Egg and larva 






6+ 
9+ 
15+ 








Pupa 
















Total 
















Urosigalphus sp. : 

Egg and larva 




12+ 
3 + 
15+ 












Pupa 
















Total 





























DISTRIBUTION OF THE PARASITES. 



61 



8. THE DISTRIBUTION OF THE PARASITES. 

Parasites of the boll weevil have been recorded from eveiy part 
of the territory so far invaded. The records are so numerous that 
we are able to show statistically which are the most important para- 
sites of the weevil. The following list gives the species in their 
numerical rank for the entire period from January 1, 1906, to Jan- 
uary 1, 1910, giving only the number which were accurately deter- 
mined for each species. The first seven species are the most important, 
as has been shown in almost every section of this report. The last 
nine species may be considered as more or less adventitious or acci- 
dental. These species may possibly never be recorded again, or, on 
the other hand, they may become in the near future among the more 
important parasites. This very event has happened in the case of 
three or four of the other more important species. Up to 1906 only 
four of the first five in this list had been recorded from the boll 
weevil. The other species have been added since and some of them 
will become very important as the weevils enter the moister wooded 
regions of the East. 

■ Tabi^e XXI. — Numerical rank of the parasites for the entire period, 1906 to 1910. 



Species. 



Microbracon mellitor 

Catolaccus hunteri 

Catolaccus incertus 

Eurytoma tylodermatis 

Cerambycobius cyaniccps. . . 
MicTodontomerus anthonom 

Tdrastkhus hunteri 

Cerambycobius cushmani. . . 

Sigalplms curcuUonis 

Habrocytus piercei 



Number 

of 
records. 



2,147 

1,094 

578 

575 

574 

302 

168 

76 

37 

36 



Species. 



Ennyomma globosa 

Lariophagus tetanus 

Myiophasia xnea 

Eurytoma sp 

Cerambycobius sp 

SpilocKalcis sp 

Urosigalphus anthonomi 

Urosigalphus sp 

Perilampus sp 

Pimpla sp 



Number 

of 
records. 



A study of the value of these parasites by years has shown that 
the majority of the species had not occupied the same rank in two 
successive years. The accompanying diagram (fig. 13), giving the 
yearly rank of the boll- weevil parasites from 1906 through 1909, 
shows that in each year new parasites were recorded and that in some 
cases these parasites continued to attack the weevil. Microbracon 
mellitor appears to vary but little in importance in different seasons, 
while Catolaccus hunteri shows increasing importance year by year. 
Some of the other parasites of considerable importance appear extremely 
variable in their relative rank. It will be noticed that Habrocytus 
piercei has occupied the ninth place three years in succession and 
is now in eighth place. This parasite occurs in small numbers, but 
may at any time become a leading parasite in Louisiana and Missis- 
sippi. In addition to giving the yearly rank of the species this 
diagram also shows the proportion of the sexes observed each year. 



62 



INSECT ENEMIES OF THE BOLL WEEVIL. 



In order to show the regions in which the various species are of 
greatest importance, the accompanying map (fig. 14) is presented. 
This shows that while Microhracon mellitor has yielded more individuals 
than the other species, it is the predominating parasite in by far the 
larger proportion of the infested territory. It can also be seen that 
much more can be expected from the other parasites as the weevil 
moves eastward into their territory. Microdontomerus anthonomi is 
quite important throughout the central black-prairie region of Texas. 
Eurytoma tylodermatis is more important in north-central Texas and 
also in the coast region of Texas, Ceramhjcohius cushmani is charac- 



1906 

<i g U l> 



1907 



B/7AC0yV »etj. ITOff 



1908 

BMCWMec I /Toff 



1909 



9 l£l> 




Fig. 13.— Diagram Illustrating yearly rank of the boll weevil parasites, 1906, 1907, 1908, and 1909. 

(Original.) 

teristic of the counties grouped around Victoria County, Tex., but a 
few specimens have been reared from the boll weevil at Alexandria, 
La., by Messrs. Cushman and Jones. 



9. THE PARASITE SEASONS. 

For the convenience of this work on parasites of the boll weevil, 
the year has been divided into definite parasite seasons correspond- 
ing with certain groups of conditions. The year opens with the 
Mhernatio7i period well underway. In so far as the parasites are 
concerned those which hibernate as immature insects mature gen- 
erally about the middle of March. This marks the end of the hiber- 



THE PAKASITE SEASONS. 



63 



nation period or winter season and the opening of the spring season. 
From March until the middle of June or sometimes July there are no 
cotton squares for the weevils to breed in. Consequently the para- 
sites are obliged to seek other hosts. The summer season is defined 
as beginning with the production of squares in which the weevils and 
their parasites may breed. Thus this season continues until squar- 
ing ceases — that is, until late in the fall when cotton is killed by frost 
and is succeeded by the winter season. However, we frequently dis- 
tinguished a fall or postmigration season, which begins with the first 




Fig. 14.— Map showing the distribution of the more important parasites of the boll weevil. (Original.) 

attack of weevils upon the bolls in August and ends with the heavy 
frosts in October or November. The fall season is also character- 
ized by a renewed growth of squares. 



I. THE HIBERNATION OR WINTER SEASON. 



The most important parasites which winter as immature stages 
upon the boll weevil are Microbraconmellitor,Catolaccus hunteri, Ceram- 
bycobius cyaniceps, Eurytoma tylodermatis, TetrasticJms hunteri, and 
Habrocytus piercei. The last two species are characteristic of 
winter examinations in Louisiana and Mississippi. The predatory 



64 INSECT ENEMIES OF THE BOLL WEEVIL. 

coleopterous larvae Hydnocera puhescens LeConte and H. pallipennis 
Say are very frequently found hibernating as larvse in the boll- 
weevil cells or in the cocoons of Microhracon mellitor. The stage in 
which these various parasites pass the winter is given very concisely 
in the table of the developmental periods (Table XX) in section 7. 
During January, 1910, Mr. Hood repeatedly found Eurytoma tylo- 
dermatis and Catolaccus Jiunteri hibernating in dry cotton squares 
and bolls and especially in hanging moss at Mansura, La. 

II. THE SPRING SEASON. 

It has been demonstrated that there is a definite period between 
the hibernation season and the first infestation of squares, extending 
from the middle of March to the middle of June. What happens to 
the parasites during this period is of considerable importance and a 
great amount of work has been done in the search for intermediate 
hosts. 

In the case of Catolaccus hunteri the question was very satisfac- 
toril}?^ answered. At Richmond, Tex., a large number of dewberry 
buds infested hy Aritlionomus sif/7iatus was gathered March 21, 1907, 
and this species of parasite was reared continuously between March 
28 and April 1 . At Victoria, Tex., Mr. J. D. Mitchell collected, on April 
23, 1907, a lot of haws {Crataegus mollis), infested by TacJiypterellus 
quadrigihhus, and on May 7 he reared this species of parasite. In- 
vestigations as to the distribution of these weevils added to the 
formerly laiown records of AntJionomus signatus in dewberry buds: 
Natchitoches and Shreveport, La.; Texarkana, Ark.; Muskogee and 
Ardmore, Okla. ; and Trinity, Richmond, Waco, Dallas, and Mar- 
shall, Tex. TacTiypterellus quadrigihhus was found breeding at 
Shreveport and Natchitoches, La., and Victoria, Tex. 

At Dallas, Tex., the buds of Galpinsia liartwegi were found to be 
infested by Auleutes tenuipes as early as April 24. This species is a 
host of several species of Catolaccus. The buds of Callirrhoe involu- 
crata were found at Dallas to be infested by AntJionomus fulvus as 
early as April 1, and on the same date Anihonomus seneolus was first 
observed to be breeding in the buds of Solanuiri torreyi. Solanum 
elseagni folium, with AntJionomus seneolus both in its buds and in the 
fungus leaf-galls, and Solanum rostratum with this weevil in the buds, 
appeared early in April. All of these plants continued susceptible to 
weevil work up to the end of the spring period, or until cotton began 
to square. Numerous specimens of Catolaccus were reared from the 
Solanum-infesting species of Anthonomus. 

MyiopJiasia senea was reared April 11, 1907, from ConotracJielus 
elegans in galls of PJiylloxera devastatrix on the petioles of Hicoria 



THE PARASITE SEASONS. 65 

pecan, collected April 2, 1907, at Victoria, Tex., and was reared June 
5, 1907, from material collected May 4 at Dallas. 

Sigalphus curculionis was reared in considerable numbers between 
April 28 and May 7, 1907, from Conotraclielus nenuphar in plums 
gathered at Texarkana, Ark., March 26; and between April 29 and 
May 17, 1907, from Conotrachelus elegans in galls of Phylloxera devas- 
tatrix on pecan, collected at Victoria, Tex., April 2; also between June 
5 and 14, 1907, from the same species in material collected at Dallas, 
Tex., May 4. 

Ceramhycohius cyaniceps was studied very carefully at Victoria, 
Tex., by Mr. J. D. Mitchell during the winter of 1909-10 as an 
enemy of Trichoharis texana in stems of Solanum rostratum, antl of 
Lixus scrohicollis in stems of Ambrosia trifida. Mr. T. T. Ilolloway 
conducted experiments in longevity by feedmg sugared water to the 
parasites. Emergence began, in the lots of Trichobaris, on February 
1 and continued until April 8. The last parasite lived until May 31. 
The total period of activity was 119 days and the average period 
lasted from March 11 to April 1. The longest record of longevity 
was 71 days and the average 21 days. Emergence began from the 
lots of Lixus on March 2 and continued until March 24. The last 
parasite lived until May 11. The total period of activity was 70 
days and the average period was between March 13 and April 4. 
The longest record of longevity was 67 days and the average 22. 

Eurytoma tylodermatis was reared from the same lots and treated 
in the same manner. Emergence began from the lots of Trichobaris 
on February 3 and continued until March 21. The last parasite 
lived until April 30. The total period of activity was 86 days and 
the average period was between March 10 and March 30. The longest 
record of longevity was 42 days, and the average 20 days. Emergence 
began from the lots of Lixus on February 22 and lasted until April 17. 
The last parasite lived until June 1. The total period of activity 
was 99 days and the average period lasted from March 16 to April 11. 
The longest record of longevity was 79 days and the average 26 days. 

III. THE SUMMER SEASON. 

TJie first boll-weevil ])arasites of the year are reared late in May or 
early in June in southern Texas, but in a very short time squares are 
forming all over the entire cotton belt and parasites may be found 
everywhere in small numbers as the summer progresses. The per- 
centage of parasitism increases rapidly and generally becomes very 
high after August 1. Most of the important parasites may also be 
found on their normal summer hosts. 
16844°— Bull. 100—12 5 



66 INSECT ENEMIES OF THE BOLL WEEVIL. 

About the middle of August squares commence to fail, and few 
squares are to be found by September 1. This condition may be 
said to begin the fall season, when the parasites are largely obliged 
to seek other hosts or to attack the boll weevil in bolls. 

IV. THE FALL OR DISPERSION SEASON. 

Coincident with the decline in square production is the begimiing 
of the boll-weevil dispersion which extends into new territory around 
the entire periphery of the infested region. In the fall there is a new 
growth of squares which furnishes food for the weevils before entering 
hibernation and also furnishes an opportunity for very high parasitism 
just preceding hibernation. It is during this season that parasite 
swarms are recorded and hence this is a very critical time for obtaining 
and transferring desirable parasites to new regions. During this early 
fall season there are several very important ways of propagating the 
parasites already present in the vicinity, as will be shown later. The 
fall season of the year closes abruptly with the first killing frost, for 
this crisis precipitates the hibernation period. 

10. ADJUSTMENT TO NEW HOSTS. 

It is a very strildng fact that the continuously breeding boll 
weevil is attacked by parasites which in many instances attack nor- 
mally weevils having but a single generation annually. Some of these 
parasites attack one host after another throughout the entire breeding 
season and may be found in activity at all periods except during 
hibernation. This condition is well illustrated by the accompanying 
diagram (fig. 15) giving the seasonal rotation of Catolaccus hunteri 
and Ceramhycohius cyaniceps. Whether these parasites were origi- 
nally single-generation species like their hosts is a question we can not 
now decide, but we now know that they have become adapted to 
many species. This fact can be most easily proven by reference to 
the list of hosts of the boll-weevil parasites given in the second section 
of this part (p. 42). It appears possible that the constantly changing 
factors of nature cause the various species to be continually adjusting 
their habits to new environments and new hosts. In other words, the 
groups of parasites from wliich the most available enemies of a new or 
introduced species may be obtained are those groups in which the 
parasitic habits are the most variable. A parasitic species that is as 
readily at home on a stem weevil as on a bud or seed weevil is probably 
able to attack many different species. 

The most striking example of the adjustment of new parasites was 
furnished in 1907. A lot of hanging squares collected by ]\Ir. J. D. 
Mitchell on August 5, 1907, at Victoria, Tex., on a field known as the 
Haskell field gave a percentage of 61.5. There was something so 



ADJUSTMENT TO NEW HOSTS. 



67 



striking about the nature of the record that Mr. C'ushman was sent 
immediately to Victoria to study the surroundings of this field and 
report upon the possible reasons for the high percentage of parasitism. 
Mr. Cushman reported after considerable study that there were 
only two factors which, it seemed to liim, might have an influence 
upon the parasites of the boll weevil. The fii-st factor was the com- 
plete lack of fruit upon the huisache trees (Vachellia farnesiana) 
which is the normal food of Laria saUsei. The second factor noticed 
was the absence of flowers on the Callirrlioe involucrata, the host of 
Anthonomus fulvus. 'Mr. Cushman reasoned that the point would be 
proven if we should rear from the boll weevil some of the character- 
istic parasites of either this or the other species. As a result of 
rearings from the material collected in this field, the prmcipal par- 
asite was Microbracon meUitor, the typical boll weevil parasite, but a 

S^ASOA/AL ROTAT/Oa/ OF HOSTS BV CaTOLACCUS HUNTERI CPAWfOffD. 



JA/VUARy 


FEBRUAfly 


MARCH 


APRIL 


. MAY- 


JCA/er 


^ULY 


AUGUST 


SEPTEMBER 


OCTOBER 


fJOVEMBER 


DECEMBER 


Anthonoi 


fUS GfiAfJ,. 


An/THCW 


OMUS S/g) 


lATi/S SAy 


ifVLus Bo. 


VCMAA/ 


■HONOMUS 


6RAAJD/6 


BOHEM^ 


AJ 




Tachw 
VS BoHEn; 


Af^THOf 


VOMUS A£/l 


-oferLws Q 


/ADR/C/B8U 


s Sav 


A/v 






Smicraui 


AX TUBEP 


:ULATC/S /■ 


/'^fljrHO^OMt^S ALBOP/L 


OSUS D/E 


fe 


ICRCULATU- 


S P/ERCE 


A 


yrno/^OMU. 


~ ncrcf>OTf 


ECAi: P/SK 




SM/Cf 


AUtAx ru, 



















SeASO/\JAL ROTAT/OAT OF HOSTS BY CsRAMBYCOB/US CYA/V/CFPS ASHMEAD. 



TACHyPTE ReLLljIS 

n 




QUAORi GI6BUS . 



1/XU3 SOfOB/COLlfe BOHEMAr j 

Smicrau^a 



AXTVBE'XWATUS PlERCE 



CfMjs soRD/pus LeCcvte 



Trichc baris CO ■JtP^CTA Casev 



A/VTl lONOMUS 



Aa/THO^OMCS GRAA/a/S BoHE/y.^M 



R/s ro'AA/A Lsao/vrE 



L/XUS SCROB/COLL.S BOHEf^.AA/ 



SM/Cf^AUlAX ThBERCaLAfl/S P/ERCl 



Fig. 15.— Diagram illustrating the seasonal rotation of hosts of Catolaccus hunteri and Cerambycobius 

cyaniceps. (Original.) 

species which is also a typical parasite of Anthonomus fulvus. It 
is probable that the latter species furnished some of the Micro- 
bracons for this infestation. The next most important species was 
Cerarnbycohius cushmani, a typical parasite of Laria sallxi and of 
Arxcerus fasciculatus which breeds in the fruit of the chinaberry tree 
{Melia azederach). In addition to this species, this same field yielded 
3 other new parasites of the boll weevil, 2 of which are known to 
be parasites of the Laria. These were Eurytoma sp., Spilochalcls sp., 
and Lariopliagus texanus. 

To illustrate the divergence of habits among parasites the host 
relations of Catolaccus incertus may be cited. This parasite attacks 
several species of Laria (Bruclius) which are internal seed eaters and 
pupate in their feeding cells; such weevils as Zygoharis lantlioxyli and 
Auleutes tenuvpes, which are seed or bud feeders and pupate in the 



68 INSECT ENEMIES OF THE BOLL WEEVIL. 

ground; and Anthonomines, which dwell in buds {Anthonomus gran- 
dis), in flowers {A. aplianostejilii) , and in hard seed (A. alhoinlosus). 
But it draws the line apparently at stem dwellers and is replaced by 
Neocatolaccus tylodermse on Lixus, Tyloderma, and Ampeloglypter. 
Ceramhijcohius cyaniceps is as much at home in a stem as in a bud, 
and so also are Eurytoma tylodermatis and Microdontomerus anthonomi. 
The Braconidse appear to be more particular as to food but the most 
noted of all, Microhracon mellitor, has no preferences between stem 
dwellers and bud dwellers. 

Thirteen miles southeast of Yazoo City, Miss., on November 1, 1909, 
the senior author found an isolated artificial focus of infestation by 
the boll weevil over 30 miles from any infestation of the same age 
and 20 miles beyond the regularly infested region. Out of 8 squares 
picked, containing 5 stages, 1 parastized stage was found. 

11. BEETLES WHICH PREY UPON THE BOLL WEEVIL. 

The attack of the insects predatory on the adult boll weevil is purely 
accidental. They may be very numerous, but the only ones recorded 
and verified are Evarthrus sodalis Le Conte and another species of the 
same genus. There are, however, several insects which have an actual 
value through their established habit of either breeding in the square 
upon the boll-weevil stages or of entering the square and consuming 
the weevil. We shall refer to four of them. 

Hijdnocera 'pallvpennis Say. A single beetle of this species was 
reared April 6, 1907, after 183 days in its cocoon, and over 214 days 
isolation in the rearing tube. It was collected in a boll-weevil cell at 
Waco, Tex., August 28, 1906. The cocoon is very finely threaded, 
loosely woven, and only single layered. The stage of the beetle can 
easily be observed at any time. 

Hydnocera pmhescens Le Conte. This clerid is a very common 
breeder in the weevil cells. Its larvse have been found not only 
feeding upon the various weevil stages but have been taken frequently 
from IVIicrobracon cocoons which they have entered at a much 
younger stage. 

Cathartus gemeUatus Duval. Tliis cucujid beetle is both a predator 
and a scavenger, its larvse being frequently found, however, feeding 
upon boll-weevil stages which they must have killed. 

Chmdiognathus spp. The larvae of these lampyrid beetles are very 
common in the squares and bolls of cotton in Louisiana and Missis- 
sippi. In one instance undoubted proof of the attack of such a larva 
upon one boll- weevil larva was recorded. Many other very sus- 
picious observations were made but no definite proofs found. 



ANTS WHICH PREY UPON THE WEEVIL. 69 

12. LEPIDOPTEROUS LARV^ WHICH ARE INCIDENTALLY PREDATORY 
UPON THE BOLL WEEVIL. 

Alabama argillacea Iliibner. The cotton leaf caterpillar is distinctly 
an enemy of the boll weevil and of considerable importance. When 
it defoliates a cotton field a month or more before the frosts it often 
destroys immature weevils in the cotton squares and cuts off the entire 
food supply of the adult weevils remaining. These weevils may be 
able to suspend their activities and begin hibernation but it is well 
known that weevils entering hibernation early in the fall can seldom 
survive a long hard winter, or live until cotton is up in the spring. 
Those that can not hibernate either die of starvation or rise in flight 
to seek cotton elsewhere and may perish in the efl'ort. It is presumed 
that a very high percentage of fljing weevils fails to find cotton. 

The leaf worm is attacked by 18 predatory bugs, 16 predatory 
beetles, 6 predatoiy wasps, and the following ants: Dorymynnex 
pijramicus jlavus McCook, Forelius maccooki Emeiy, Solenojms 
geminata Fabricius (these three ants are enemies of the boll weevil) 
and Monomoi'ium carhonarium. Smith. Ten hymenopterous parasites 
and one hyperparasite are known, and in addition the leaf worm is 
attacked by a predatory fly and by two parasitic flies. 

13. ANTS WHICH PREY UPON THE BOLL WEEVIL. 

HYMENOPTERA. DORYLID.E. 

Eciton (Acamatus) commutatum Emeiy. This ant was taken by 
Mr. C. R. Jones at Beeville, Tex., attacking the boll- weevil larvae in 
squares. Dr. W. M. Wlieeler states that it is commonly parasitized 
by a round worm of the genus Mermis. 

PONERID^. 

Edatomma tuberculatum Olivier. The "kelep," or so-called Guate- 
malan ant, is a native of Mexico and Central America. Like all other 
ponerids it is slow in action. The mnters have proven too severe 
for any of the imported colonies. The rate of development is so 
slow and the movements of the adults are so sluggish that little 
could be hoped for from this species even if it could become accli- 
mated in this countiy. 

MYRMICID.E. 

Cremastogaster lineolaia (Say) var. clara Mayr. This ant is also an 
enemy of the boll weevil, having been recorded attacldng immature 
stages at Dallas, Tex., by Dr. W. E. Hinds. It has frequently been 
seen in the rearing cage carrying off insect prey. The species lives 



70 



INSECT ENEMIES OF THE BOLL WEEVIL. 



in hollow stems, sticks, and galls and is commonly seen at the necta- 
ries of cotton or attending aphides, membracids, etc. Prof. F. E. 
Brooks has recorded this ant as an enemy of Heliotliis obsoleta, the 
cotton boll worm. 

Solenopsis geminafa Fabricius. The ''fire ant" (fig. 16) is very 
common in Texas cotton fields, where it is always an enemy of the 
boll weevil, as well as of the cotton bollworm {Heliotliis obsoleta) 
and tlie cotton leaf worm {Alabama argiUacea). In Louisiana, 
Arkansas, and Mississippi it is very seldom seen in cotton fields, 
except in soiitliern Louisiana, where unfortunately it is in danger of 
extermination by the Argentine ant, Indomyrmex hmnilis Mayr. 
This species divides credit for the greater part of the ant control of 
the boll weevil with the other species of Solenopsis, two species of 

Monomorium, and with the various spe- 
cies of Pheidole. Its nests are placed in 
the cotton fields, generally near the base 
of the plants, and from these the foragers 
go out in all directions in search of food. 
The workers have learned to detect the 
presence of the boll weevil in the squares 
and in a short time can effect an entrance 
into the wee^nl cell from which they either 
draw the weevil bodily or convey it in 
parts to their nests. This ant is some- 
times found on the plant, but most com- 
monly it does its work on the ground. 
The species is parasitized by {Pseudac- 
teon) Plastoyliora crawfordi Coquillett at 
Dallas, Tex. 

Solenopsis molesta Say {dehilis Mayr) . 
This minute ant was taken in the act of 
attacking a boll-wee^dl larva by Mr. Cushman at McAlester, Okla. 
This species and the next are so similar in appearance that they 
may be easily confused. Prof. F. E. Brooks has recorded it as an 
enemy of Craponius insequalis. 

Solenopsis texana Emeiy. This minute ant is a common enemy 
of the boll weevil in Texas, Louisiana, and Mississippi. The entrance 
holes are very minute, but sometimes the ants enter the squares in 
great numbers. On October 31, 1907, at Thornton, Tex., Mr. 
Cushman found 85 individuals attacking a weevil larva in a single 
square. It is mentioned in the investigation records as attacking 
the weevil at Alexandria and Monroe, La., and Cuero, Lampasas, and 
Llano, Tex. It is also recorded as an enemy of Heliotliis obsoleta. 

Monomorium 7ninimmn Buckley. This common house ant (fig. 17) 
is a very valuable enemy of the boll weevil and is common in cotton 




Fig. ]6.— The "fire ant" {Solenopsis 
geminata), an enemy of the boll 
weevil: Worker. Enlarged. (From 
HiTnter and Hinds.) 



ANTS WHICH PREY UPON THE WEEVIL. 



71 



fields. It is recorded in the Dallas collection as attacking the boll 
weevil at Llano, Lampasas, Albany, Henrietta, Arlington, and Dallas, 
Tex., Euston, La., and Roxie and Port Gibson, Miss. The species 
has been taken attacking the immature stages of Trichobaris com- 
jyada, Antlionomus alhopilosus, and Anthonomvs fidvns. It generally 
attacks these weevils as well as the boll weevil on the plant, entering 
the infested bud or square in search of its food. 

Monomonum iDliaraonis L. This cosmopolitan house ant (fig. 18) 
is another of the most important boll-weevil enemies, being very 




Fig. 17.— The little black aiU (Mundinoriiim minimuin), an euemy of the boll weevil: a. Fe- 
male; 6, same with win^s; c, male; d, workers; e, pupa; /, larva; g, egg of worker. 
Enlarged. (From Marlatt.) 

abundant in the cotton fields of certain sections. It is represented 
in the Dallas collection as attacking the boll weevil at Victoria, Tex.; 
Fosters, Ruston, and Monroe, La., and Camden, Ark. It also 
attacks the weevil on the plant. In southern Louisiana it is being 
exterminated by the Argentine ant (Iridomyrmex Jiumilis). 

Pheidole sp., near Jlavens. At Arlington, Tex., August 31, 1908, 
Mr. Cushman found abundant evidence of the control of the boll 
weevil by this species. It attacks the weevil larvae both on the 
plant and on the ground. 



72 INSECT ENEMIES OF THE BOLLi WEEVIL. 

Pheidole crassicornis Emery. At Lampasas, Tex., September 23, 
1908, Mr. Ciishman found this ant a very abundant enemy of the 
boll weevil. 



DOLICHODERIDiE. 



Forelius maccooH Forel. At Beeville, Tex., August 13, 1906, Mr. 
C. R. Jones found a high mortality of the boll weevil due to this 
species. Dr. Wlieeler has recorded the fact that this ant prefers 
bare, dry ground for its nests. The species also attacks Alabama 
argillacea and Heliothis ohsoleta. On September 7, 1908, at Dallas, 
Tex., Mr. F. C. Bishopp took specimens in the act of attack, and 
September 21, 1908, Mr. Cushman took others at Llano, Tex., attack- 
ing the weevil. 

Dorymyrmex injra.inicMs Roger, the "lion ant," protects solitaiy 
tree cotton from the boll weevil in Cuba (Schwarz, 1905). 





Fig. 18. — The little red ant {Monomoriwm pharaonis), an enemy of the boll weevil: 
a, Female; b, worker. Enlarged. (From Riley.) 

Dorymyrmex pyramicus (Roger) var. flavus McCook. This com- 
mon ant of the cotton fields has only once been taken as an enemy 
of the boll weevil, namely at Texarkana, Tex., by Mr. R. C. Howell, 
but its abundance would make it a very important species if it 
should develop a fondness for weevil larvse. It is an enemy of 
Alabama argillacea and Heliotliis obsoleta. 

Iridomyrmex analis Andre. Specimens of this ant were found 
attacking the boll weevil by Dr. W. E. Hinds. This species is nor- 
mally a honey ant, but occasionally takes insect food. It is veiy 
common in cotton fields, especially in Louisiana. 

Iiidomyrmex humilis Mayr. The much-feared Argentine ant has 
been taken attacking the boll weevil. It is, however, a friend to 
the weevil because it exterminates Solenopsis geminata, Monomorium 
pharaonis, smd Iridomyrmex analis (Foster, 1908). 



BIOLOGY OF TPIE COHOSTS. 73 



FORMICIDiE. 



Formica fusca (Linnaeus) suhpolita (Mayr) perpilosa Wheeler. This 
species of ant is normally a honey feeder, but it is recorded by Rangel 
(Rangel, 1901c) as a predator on adult boll weevils in Mexico. 

Formica pallidi-fulva Latreille. A single instance of this species 
cutting its way into a square infested by a boll weevil was observed 
by Mr. Hood at Ashdown, Ark., September 2, 1908. 

Prenolepis imparis Say. A single instance of this species cutting 
its way into a square infested by a boll weevil was observed by Mr. 
Hood at Ashdown, Ark., September 2, 1908. 

14. BIOLOGY OF THE COHOSTS OF THE BOLL-WEE^^L PARASITES. 

The biologies of the parasites concerned in the boll-weevil complex 
have already been discussed. It now remains to consider the native 
weevils which have already or may later enter into the complex of 
cohosts of the boll-weevil parasites. Many of these weevils are 
native to the territory already occupied by the v-eevil, while others 
will become important as new territory is added. Other families of 
Coleoptera and even other orders of insects may later be found to be 
of more or less importance as cohosts of boll- weevil parasites. The 
late Dr. William H. Ashmead stated that Microhracon meUitor had 
been reared from many Coleoptera, while Ceramhycohius cyaniceps 
bred in cerambycids and other beetles. It is important also to note 
the record of Ceramhycohius cyaniceps from Languria. Our own 
observations have been confined to the Coleoptera of the families 
Lariidse, Anthribidas, and Curculionidse. 

PHYTOPHAGA. LARIID^. 

(BrudiusY Laria sallxi Sharp. Tliis bruchid is characteristic of 
the Gulf Coast prairie of Texas. It breeds in the pods of huisache 
( VacJielliafarnesiana) , is a continuous breeder, and is generally highly 
parasitized by Urosigalplius hruclii, Ceramhycohius hruchivorus , Cer- 

AMBYCOBIUS CYANICEPS"; CeRAMBYCOBIUS CUSHMANI, LaRIOPHAGUS 

TEXANUS, EuRYTOMA TYLODERMATis, Horlsmeuus sp., and several 
other undetermined parasites. 

Laria exigua Horn. This bruchid is apparently Austroriparian and 
Carohnian. Its principal food plant is Amorphafruticosa, in the seed 

1 The generic name Bruehus was first used bj' Geoffroy in 17G2. Only one species is admissible in our 
code of nomenclature and this is C erambyx f ur'Lhm.xxis, which is also the type of Ptinus Linnaeus 1707. 
The genus Laria was described by Scopoli in 1703 and the type thereof has been designated as salicis 
Scopoli, a synonym of Derincstes pisorum (pisi) I^innteus. 

Linnseus's conception of Bruehus dates from 1707 and the type thereof was designated by Latreille 
(1810) as Dcrmestes pisorum Linnasus. Hence we see that Bruehus Linnaeus (1758) Is preoccupied by 
Geoflroy (1752) and an isogenotypic synonym of Laria Scopoli (1703). 

Although the genus has been subdivided into several genera, our American species have not been 
studied with regard to such subdivision and it is hence best to consider all as iu the genus Laria, 
sensu latiore. 

s The names of boll-weevil parasites are printed in small capitals; others in itaUcs. 



74 



INSECT ENEMIES OP THE BOLL WEEVIL. 



pods of which it breeds prohfically. It is a continuous breeder and 
is highly parasitized by Ceramhycohius hrevicaudus , Cerambycobius 
CYANiCEPS, Ilorismenus sp., Reterosiy'tlus 'prosoindis, Eurytoma sp., 
MiCRODONTOMERus ANTHONOMi, Catolaccus incertus, and Several 
other species. 

Laj'ia ohtecta Say. The common bean v.'^ecvil is known to be para- 
sitized by Cerambycobius cyaniceps and Bruchohius laticolUs. 

Laria comfressicornis SchaefFer. This bruchid, which breeds in 
the pods of Acuan illinoensis , is parasitized by Cerambycobius cy- 
aniceps and Heterospilus prosojndis. 

Laria ocliracea Schaeffer. This bruchid, which breeds in the pods 
of Vicia sp., is parasitized by Cerambycobius cyaniceps, C. cush- 
mani, Eurytoma sp., and Heterospilus j^rosopidis. 

Spermophagus rohinke SchaefTer. This bruchid is very common in 
the pods of the honey locust (Gleditsia triacantlios) , and the water 
locust {Gleditsia aquaiica), both of which are trees belonging to the 
humid Austral zones. It is parasitized by Heterospilus hrucJii, Cer- 
ambycobius cyaniceps, Eurytoma tylodermatis, and TJrosigalpJius 
hrucM. 

RHYNCHOPHORA. ANTHRIBID.K. 

BracJiytarsus alternatus Say. This beetle probably breeds under 
many different circumstances. The only records are from a fungus 
gall on Ipomcea pandurata, and from the stems of Elymus virginicus 
and Sideranthus rubiginosus. It apparently belongs to the humid 
Austral zones. It is parasitized by Microdontomerus anthonomi 
and a Bracon. 

Arsecerus fasciculatus DeGeer. This very mdely distributed 
Lower Austral insect (see fig. 19), known commonly as the coffee- 
bean weevil, 
breeds in stored 
vegetable prod- 
ucts, in the seed 
of TTieohrojna 
cacao, in the 
berry of the coffee 
tree {Coffea ara- 
bica), in diseased 
cotton bolls, in 
seed pods of 
Cassia occident- 
alis and C. oh- 
tusifolia, in seeds 

of Indigqfera tinctoria, in green and decaying fruit of Melia azedarach, 
in green and dry cornstalks, and in dry acarian galls on Ipomcea 




Fig. 19. — The coffee-bean weevil (Arscccnis fasciculatus) , a cohost of boll- 
weevil parasites: a, Larva; b, adult; c, pu\rA. Enlarged. (From Chit- 
tenden.) 



BIOLOGY OF THE COHOSTS. 



75 



lacunosa. In the Melia berries it is parasitized by Cerambycobius 

CUSHMANI, EURYTOMA TY'LODERMATIS, and PeDICULOIDES Sp. 



CURCULIONID.E. APIONIN.E. 

Apion seg.ni'pes Say in Cracca virginiana is parasitized by Eury'- 

TOMA TYLODERMATIS. 

A'pion decoloratum. Smith. Dr. Cliittenden records this weevil as 
breetUng in Meihomia paniculata and parasitized by Catolaccus 

INCERTUS. 

A'pion griseum Smith. Dr. Chittenden records this weevil as 
breeding in Phaseolus retusus, P. wriglitii, P. polystachyus, and 
StropJiostyles paucifiora, and parasitized by Catolaccus incertus. 

Apion nigrum Smith. Breeds in buds of Rohinia pseudacacia and 
is parasitized by Catolaccus incertus. 

Apion rostrum Say in pods of Baptisia is parasitized by Ceramby'- 

COBIUS CYANICEPS. 

CLEONIN^. 

Lixus musculus Say. This weevil is known both from the Lower 
Sonoran and Austroriparian zones. It breeds in the stems of Poly- 
gonum pennsylvanicum, P. portoricense, and P. 
punctatum, maldng an oblong gall or swelling. 
It is parasitized by Eury^toma ty'lodermatis, 
Ceramby'cobius cy'aniceps, Neocatolaccus 
tylodermx, GlyptomorpTia rugator, G. novitus, 
and Horismenus lixivorus. 

Lixus scrohicoUis Boheman. Tliis weevil (fig. 
20) is probably confined mainly to the moist 
Austral zones. It breeds abundantly in the 
stems of Anibrosia trijida, A. artemisisefolia, 
A. psilostacJiya, and Ilelianthus spp. It is 
c[uite highly parasitized hy Ptinohius magnijicus , 

EURY'TOMA TYXODERMATIS, CeRAMBYCOBIUS 

CY^ANiCEPs, Glyptomorpha rugator, G. mavaritus, 
G. lixi, Vipio helfragei, Microdus simillimus, 
and Horismenus lixivorus. Mr. Townsend has 

described Lixopliaga parva from a specimen reared from this weevil 

at Dallas, Tex., August 15, 1907. 




Fig. 20.— The blood weed 
weevil (jLijhs scrobicollis) , a 
cohost of boll-weevil para- 
sites. Enlarged. (From 
Hunter and Hinds. 1 



ERIRRHININ^. 



Smicronyx tycTioides LeConte. This weevil breeds in stem galls of 
various species of Cuscuta. It is parasitized by Microbracon mel- 
LiTOR and Eutrichosonia alhipes. 



76 



INSECT ENEMIES OP THE BOLL. WEEVIL. 



Desmoris scapalis LeConte. This weevil (fig. 21) occurs mainly 
on the black prairie in Texas and breeds in the heads of SiderantTius 
ruhiginosus. It is parasitized by Microbracon mellitoe. 

ANTHONOMIN.E. 

Macrorlioptus sphseralcix Pierce. This weevil was found breeding 
in stems of Sphseralcea angustifolia. It is the host of Eurytoma 

TYLODERMATIS. 

TacJiypterellus guadrigihhus Say. This fruit weevil breeds in the 
seed of apple, pear, Cratsegus oxyacantha, and Cratxgus mollis. It is 
known to us to be parasitized by Cerambycobius cyaniceps and 
Catolaccus hunteri. 

Smicraulax tuherculatus Pierce. This species breeds in the stems 
of mistletoe (Phoradendron iiavescens) throughout Texas, and evi- 
dence of its work has been observed in Louisiana and Mississippi. It 

is parasitized by Eurytoma tylo- 
DERMATis, Cerambycobius cyani- 
ceps, Catolaccus hunteri, and 
jMicrobracon mellitor. 

Anthonomus fiilvus LeConte. 
This weevil breeds in the larger 
l^uds of Callirrhoe involucrata and 
C. digitata. It is a characteristic 
woodland and meadow insect in 
Oklahoma and Texas . The known 
parasites are Catolaccus incer- 
Tus and Microbracon mellitor. 
Anthonomus signatus Say. The 
strawberry Aveevil is mainly char- 
acteristic of the humid Austral zones, and it breeds in the buds of 
strawberry, blackberry, dewberry, raspberry, Rubus viUosus, Poten- 
tilla canadensis, and Cercis canadensis. It is parasitized by Micro- 
hracon anihonomi, Calyptus tihiator, Catolaccus hunteri, C. incer- 
tus, and C. anthonomi. The two latter species were described from 
this weevil. 

Anthonomus cdhopilosus Dietz. This little Texas weevil breeds in 
the capsules of Croton capitatus, O. engelmanni, and C. texense. It 
is known to us to be parasitized by Microbracon mellitor, Cato- 
laccus hunteri, C. incertus, and Cerambycobius cyaniceps. 

Anthonomus nigrinus Boheman. This species is eastern in habitat 
and breeds in the buds of Solanum carolinense, and the potato {S. 
tuberosum). It is the host of Entedon lithocoUetidis, Eriglyptus 
rohustus, Catolaccus incertus, and C. anthonomi. 




Fig. 21.— The iroiiweed weevil (Desmoris sea. 
palis), a cohostof boU-weevil parasites. En- 
larged. (From Hunter and Hinds.) 



BIOLOGY OF THE COHOSTS. 



77 



Anthonomus seneolus Dietz. Tliis Texas weevil breeds commonly 
in fungus galls on the leaves and in the buds of Solanum eleagnifolium 
and S. torreyi and also in the buds of S. rostratum. It is parasitized 
by Catolaccus hunteri and a Eurytoma. 

Anthonomus eugenii Cano (xneotinctus Champion). The pepper 
weevil (fig. 22) breeds in most of the cultivated and wild peppers 
and may be considered a serious pest. It is parasitized by Catolac- 
cus HUNTERI, Microbracon mellitor, and Pediculoides ventri- 
cosus. 

Anthonomus squamosus LeConte. Tliis is a weevil typical of the 
gypsum prairie of the Lower Sonoran Zone, although occurring less 
abundantly in the western edge of the moist Austral zones. It 
breeds in the flower heads of Grindelia squarrosa nuda, G. inuloides, 
and perhaps also on other Grindelias and Heliantlii. It is known 
to us to be parasitized by Microbracon 
mellitor, Catolaccus iiunteri, and Eury- 
toma TYLODERMATIS. 

Anthonomus nebulosus LeConte. This wee- 
vil breeds in the buds of Crataegus in Louisi- 
ana and Arkansas. It is parasitized by Cato- 
laccus HUNTERI and Sigalphus sp. 

Anthonomus heterothecx Pierce. This small 
weevil breeds in the flower heads of Hetero- 
theca suhaxillaris and probably other asteroid 
flowers. It is parasitized by Catolaccus 
HUNTERI and Eurytoma tylodermatis. 
Previous records by the senicn* author on 
Anthonomus disjunctus LeConte all refer to 
this weevil. 

Anthonomus aphanostephi Pierce. This weevil breeds in the heads 
of Aphanostephus slirrohasis, and is parasitized by Catolaccus 
incertus. 




Fig. 22.— The pepper weevil 
{Anthonomus eugenii) , a cohost 
of boll-weevil parasites. En- 
larged. (From Hunter and 
Hinds.) 



TYCHIIN.E. 



Tycliius sordidus LeConte. This Austroriparian weevil breeds in 
the pods of Boptisia hracteata and i>. leucantha. It is ])arasitized 
by Cerambycobius cyaniceps. 



CRYPTORHYNCniN^. 



Chalcodermus seneus Boheman, the common cowpea weevil (fig. 23), 
is abundantly parasitized by Ennyomma globosa, and is likewise a 
host of Ennyomma clistoides and Sigalphl^s curculionis. 

Conotrachelus affinis Boheman. This weevil breeds in hickory nuts 
and is parasitized by Myiophasia iENEA and Sigalphus curculionis. 



78 



INSECT ENEMIES OF THE BOLL WEEVIL. 




Fig. 23.— The covvpea weevil {Chalcodermus seneiis), a cohost of 
boll-weevil parasites. Enlarged. (From Chittenden.) 



Contraclielus juglandis LeConte. This is the walnut weevil, wliich. 
is also parasitized by Myiophasia .^enea, Cliolomyia inxquii^es, Meta- 
dexia lasalis, and Sigalphus cuhculionis. 

ConotracJielus elegans Say. This weevil breeds abundantly in 
the petioles of hickoiy, the galls of Phylloxera devastatrix on pecan, 

in pecan nuts, in leaf 
rolls on liickory, and 
finally in the roots 
of Amaranthus retro- 
jiexus. It is fre- 
quently parasitized 
by Myiophasia ^nea 
and Sigalphus cur- 
cuLiONis, and occa- 
sionally by Cliolomyia 
insequipes. 

ConotracJielus nen- 
uphar Herbst. The 
common plum curculio (fig. 24) breeds in the pulp of drupes and 
pomes. The larvse are parasitized by Cholomijia inxquipes, Sigal- 
phus cuRCULiONis, MicROBRACON MELLiTOR, and Povizon conotracheli, 
and the eggs by Anaphes conotracheli. 

ConotracJielus naso Le- 
Conte. The common 
acorn weevil is para- 
sitized by Sigalphus 

CURCLTLIONIS. 

Tyloderma foveolatum 
Say. This common wee- 
vil breeds prohfically in 
the stems of Onagra hien- 
nis and Epilobium. It 
is liighly parasitized by 
Neocatolaccus tylodermse, 
Cerambycobius cyan- 
iceps, eurytoma ty- 

LODERMATIS, MiCROBRACON MELLITOR, SiGALPHUS CURCULIONIS, and 

Urosigalphus sp. no v. 

GerstsecTceria nohilis LeConte (Acalles). The common pricldy-pear 
weevil is parasitized by Catolaccus hunteri and by several other 
species. 




Fig. 24. — The plum cureuMo (Conotrachelus nenuphar), & cohost 
of boll-weevil parasites: a, Larva; b, adult; c, pupa. Much 
enlarged. (From Chittenden.) 



BIOLOGY OF THE COHOSTS. 



79 



CEUTORHYNCHIN^. 



Auleutes tenuipes LeConte. Tliis weevil breeds in the anthers of 
buds of Galpinsia hartwegi on the Texas black prairie at least. It is 
attacked by Catolaccus incertus, Microhracon sp., Eutrichosoma 
alhipes, and possibly by Catolaccus nigrosenea. 

Crajjonius inxqualis Say. This weevil breeds in the fruit of the 
grape. It is parasitized by Microbracon mellitor and Stiboscopus 
hrooksi. 

Khinoncus pyrrhopus Boheman. Tliis weevil breeds in the stems 
of Polygonum and is parasitized by Cerambycobius cyaniceps. 

Ceutorhynchus n. sp. Tliis weevil breeds in the crown of Selenia 
aurea and is parasitized by Catolaccus incertus. 



Baris cuneipennis Casey. This weevil breeds in the roots of 
Helenium tenuifolium and is parasitized by Catolaccus incertus. 

Orihoris crotchii LeConte. This 
Lower Sonoran weevil breeds in the 
seed pods of Mentzelia nuda. It is 
parasitized veiy higlily by Microhracon 
nuperus, Eurytoma tylodermatis, 
and a species of Totrastichus. 

TricJioharis texana LeConte. Tliis 
species breeds very abundantly in 
stems of Solanum rostratum., and is 
hence more or less a Lower Austral 
insect. Its parasites are Cerambyco- 
bius cyaniceps, Eurytoma tyloder- 
MATis, Microbracon sp., and Sigal- 

PHUS CURCULIONIS. 

Trichoharis trinotata Say. The po- 
tato stalk weevil (fig. 25) breeds in 
the stems of many Solanacete, includ- 
ing Solanum. carolinense, S. melongcna 
(egg plant), 8. rostratum, S. tuberosum 
(potato), Datura stramonium, D. tatula, Physalis longifolia, P. philadel- 
pJiica, P. lanceolata, P. Jieteropliylla, and P. virginiana ambigua. It is 
known to be parasitized by Sigalphus curculionis and Eurytoma 

TYLODERMATIS. 

TricTiobaris compacta Casey. This weevil breeds in the pods of 
Datura stramonium and is also recorded as breeding in Datura mete- 
loides. It is parasitized by Ceraisibycobius cyaniceps, Myiophasia 
.aJNEA, and Pediculoides ventricosus. 




Fig. 25.— The potato-stalk weevil ( Tricho- 
baris trinotata), a cohost of boll-weevil 
parasites: o, Beetle; 6, larva from side; 
c, pupa; d, section of potato stalk opened 
to show larva and pupa in situ, a, b, c, 
Five times natural size; d, natural size. 
(From Chittenden.) 



80 



INSECT ENEMIES OF THE BOLL, WEEVIL. 



AmiJeloghipter sesostris LeConte. The grapevine gall weevil is para- 
sitized by Myiophasia ^nea, Neocatolaccus tylodermse, and Calyptus 
tibiator. 

Zygoharis xantlioxyli Pierce. This weevil is abundant in the berries 
of X antlioxylum clava-lierculis. It is parasitized by Catolaccus 

HUNTERI and SiGALPHUS CURCULIONIS. 



BALANININ.E. 



Balaninus nasicus Say. Tliis weevil breeds in acorns. It is para- 
sitized by Myiophasia ^nea and possibly by Trichacis rujipes. 



CALANDRIN^. 




Cdlandra oryza Linnjeus. The cosmopolitan rice and corn 
weevil (fig. 26) breeds in acorns of several species of oak, in galls of 

Phylloxera devastatrix on Hicoria pecan, in 
old cotton bolls, and in all kinds of stand- 
ing and stored grain. It is parasitized by 
Meraporus calandrse, M. vandinei, M. uti- 
hilis, M. requisitus, and Catolaccus in- 
CERTUS. Other parasites have been re- 
ported abroad. 

15. A LIST OF THE HOST PLANTS OF THE 
COHOST WEEVILS. 

In order to show more plainly the num- 
ber and variety of plants whose presence around the cotton field, 
if infested by their typical weevils, would influence the parasite 
control of the b(dl weevil, the following list is i:>resented, using the 
classification of Britton (1901): 



Fig. 26.— The rice weevil ( CWawZro 
oryza), a cohost of boll-weevil 
parasites. Enlarged. (From 
Chittenden.) 



Plant. 



Triticiim sativum (wheat) . . 
Elymus virginicus 

Zca m.ais (corn) 

Oryza fatiin (rice) 

Jiiglans nigra (walnut) 

Hicoria sp. (hickory) 

Hicoria alba (hickory) 

Hicoria pecan (pecan) 

Quercus spp 

Phoradendron flavescerv^ 

Polygomtm penm^ylianicmu 
rolygonuin portoricense 

Polygonum punctatum. . . . 

Ainaranthas retrofiexus. 



Infested by- 



Calandra oryza I.. 

Anthrihufi alternatiLs Say. 
{ Anv cents faf^ciculalus DeG. 
\ Calandra oryza L. 

Cahmdra oryza. j, 

Coiiotrachfliis jvgtandis Lee. 

Conotrachdus ajjinis Boh. 

Conotrachelus elegans Say. 

Conotrachclus elegans. 
(Balaninus spp. 
I Conotrachclus naso Lee. 
[Calandra oryza Ij. 

Smicravlox tuherculalux Pierce. 

Lixus viusculus Say. 

Lixus musculus. 

Lixus musculus. 

Rhinoncus pyrrhopns Boh. 

Conotrachelus elegans Say. 



HOST PLANTS OF COHOST WEEVILS. 



81 



Plant. 



Selenia aurea 

Rubiis villosus (blackberry) 

Rubus tiirialis (dewberry) 

Rubus occidrntalis (raspberry). . . . 
Fragaria liryiniana (strawberry).. 

Potentilla canadensis 

Pyrus communis (pear) 

Mains malus (apple) 

Cratsegus mollis (haw) 

Cratsegus oxyacantha 

Prumis (plum) 

Amygdalis persica ( peach ) 

Amygdaiis persica (nectarine ) 

Amygdalis armcniaca (apricot ) 

Vachcllm farnesiana (huisache) . . . 

Acuan illinoensis 

Strombocarpris (screw-bean) 

Prosopis glandulosa (mesctuite). . . 

Cercis canadensifi (redbud) 

Cassia obtusifolia 

Cassia occidcntalis 

Gleditsia aqyatica (water locust). . . 

Gleditsia triacanthos (locust) 

Vigna ungniculata (cowpea) 

Baptisia bracteata 

Baptisia leucantha 

Baptisia tinctoria 

Amorphafruticosa 

Indigofera tincforia 

Cracca virginiana 

Robinia pseudacacia 

Vicia sp 

Meibomia paniculata 

Phaseolus polystachyus 

Phaseolus retiisus 

Phaseolus wrightii 

Phaseolus vulgaris (bean ) 

Phaseolus vulgaris 

Strophostylus pauciflora 

Xanthoxylum clavn-herculi'i 

Melia azedarach (China tree) 

Croton capitatus 

Croton engelmanni 

Croton texense 

Vitis spp. (grape) 

Callirrhoe digitata 

Callirrhoe involucrata 

Sphseralcea angustifolia 

Gossypiuin Mrsutum (cotton) 

Mentzelia nuda 

Opuntia (prickly pear) 

Opuntia engelmanni 

Epilobium sp 

Gaura sp 

Onagra biennis 

16844°— Bull. 100—12 6 



Infested by- 



Ceutorhjnchus sp. 

Anthonomus siguatus Say. 

Anthonomus signatus. 

A ntho no m us signal u s . 

Anthonomus signatus. 

Anthonomus signatus. 

Tachypterellus quadrigibbus Say. 

Tachy ptcrellus quadrigibbus^. 
j Tachypterellus quadrigibbus. 
[Aiithonomus nebulosus Lee. 

Tachypterellus quadrigibbus Say. 

Conotrachelus nenuphar Hbst. 

Conotrachelus nenuphar. 

Conotrachelus nenuphar. 

Conotrachelus nenuphar. 

(Bruchus) Laria salLri Sharp. 

Laria bisignata Horn. 

Laria prosopis Lee. 

Laria prosopis. 

Anthonomus signatus Say. 

Arcccerus fasciculat us DeG . 

Arsecerusfasciculattis. 

Spermophagus robinix Schon. 

Spermophagus robinix. 

Chalcodermus seneus Boh. 

Tychius sordidus Lee. 

Tychius sordidus. 

Apion rostrum Say. 

Laria exigua Horn. 

Arxcerus fasciculatus DeG. 

Apion segnipes Say. 

Apion nigrum Sm. 

Laria ochracea Schaeff. 

Apion decoloratum Sm. 

Apion griseum, Sm. 

Apion griseum. 

Apion griseum. 

Chrdcodcrmus f^eneus Boh. 

Laria obtecta Sny. 

Apion griseum Sm. 

Zygobaris xanthoxyli Pii'rce. 

A r<rcerus fascicu latvs D i e t z . 

Antho7io7nus albopilosus Dietz. 

Anthonomus albopilosus. 

Anthonomus albopilosus. 
(Ampeloglypter sesostris Jjec. 
[Craponius inxqualis Say. 

Anthonomus fulvus Lee. 

Anthonomus fulr us . 

Macrorhoptus sphseralci;v rierce. 
(Anthonomus grandis Boh. 
I Arseccrus fasciculat us DeG . 
I Chalcodermus xneus Boh. 
I. Calandra oryza L. 

Orthoris crotchii Lee. 

Gerstxclceria nobilis Lee. 

Gerstaeckeria nobilis. 

Tyloderma foveolatum Say. 

Languria sp. 

Tyloderma foveolatum Say. 



82 



INSECT ENEMIES OF THE BOLL WEEVIL. 



Plant. 



Galpinsia hartwegi 

Ipomoca lacunosa 

Ipomcca pandnrata 

Physalis heterophylla 

Phijsalis lanceolata 

Physalis longifolia 

Physalis philadelphica 

Physalis virginiana ambigiia 

Solarium carolinense 

Solaniim eleagnifolium 

Solarium heterodoxum 

Solanum melongena (egg plant) 

Solanum rostratum 

Solarium rostratum, 

Solanum torreyi 

Solanum tuberosum (potato) 

Capsicum annuum, (pepper) . . . 
Datura stramonium 

Datura tatula 

Ambrosia artemisix folia 

Ambrosia psilostachya 

Ambrosia trifida 

Grindelia inuloidcs 

Grindclia squarrosa nuda 

Ueterotheca subaxillaris 

Aster salicifolius 

Sideranthus rubiginosus 

Sideranthus rubiginosus 

Aphanostfphus skirrobasis 

Helianthus spp. (sunflower) 

Ilelenium tenuifolium 



Infested by- 



Auleutes tenuipes Lee. 
Arxcerus fasciculatus DeG. 
Brachytarsus alternatus Say. 

Trichobaris trinotata Say. 

Trichobaris trinotata. 

Trichobaris trinotata. 

Trichobaris trinotata. 

Trichobaris trinotata. 

Trichobaris trinotata. 
Anthonomus nigrinus Boh. 
Anthonomus seneolus Dietz. 

Ti-ichobaris texana Lee. 

Trichobaris trinotata Say. 

Trichobaris texana Lee. 
Anthonomus seneolus Dietz. 
(Anthonomus asneolus. 
[Trichobaris texana Lee. 
(Anthonomus nigrinus Boh. 
[Trichobaris trinotata Say. 
Anthonomus eugenii Cano. 
(Trichobaris trinotata Say. 
[ Trichobaris compacta Casey. 

Trichobaris trinotata Say. 
Lixus scrobicollis Boh. 
Lixas scrobicollis. 
Lixus scrobicollis. 
Anthonomus squamosus Leo. 
Anthonomus squamosus. 
Anthonomus hctcrothecx Pierce. 
Anthonomus aphanostephi Pierce. 
Desmoris scapalis Lee. 
Brachytarsus alternatus Say. 
Ayithonomus aphanostephi Pierce. 
Lixus scrobicollis Boh. 
Baris cuneipennis Casey. 



16. A SUMMARY OF THE MORE IMPORTANT BIOLOGICAL FACTS. 

1. The boll weevil has 54 enemies, including parasites and predators. 

2. These enemies are native to other insects wliich are to be found 
in the vicinity of cotton fields. 

3. The interrelationships of the boll weevil and its parasites with 
surrounding insects are very complicated. 

4. The parasites are sometimes found in great numbers. 

5. The cotton plant, by its production of nectar, furnishes a very 
powerful attraction for parasites and predatory insects. 

6. The development of the boll- weevil parasites is as rapid as that 
of the boll weevil. 

7. Most of the parasite species are well distributed. 

8. The parasite species attack other hosts in the spring and have 
a generation before the boll weevil is ready for them. 

9. New species of parasites are becoming adapted to the weevil 
each year. 



ECONOMIC PKINCIPLES INVOLVED. 83 

10. Other cotton insects, by their ravages upon tlie food of the 
weevil, sometimes reduce the numbers of the boll weevil itself. 

11. Much valuable work is done by the ants, wMch are present in 
many fields. 

PART III. THE ECONOMIC APPLICATION. 

The economic application of ])arasitic control to the boll-weevil 
problem is dependent upon accurate knowledge of a multitude of 
conditions. The preceding two parts of this bulletin have been 
devoted to a statement of the many phases of the parasite situation. 
It must be understood at the beginning of this part that we consider 
the utilization of parasites and other insects inimical to the boll 
weevil as intimatelv connected with good agriculture. The boll- 
weevil j)roblem, from a parasite standpoint, is entirely different 
from any other parasite problem ever studied. In other cases such 
means as introductions from foreign countries may be utiUzed. In 
the present case the main problem is to debase such agricultural 
practices as A\d]l increase the effectiveness of the parasites already 
present. 

In order to facihtate the treatment of tlie economic methods to be 
suggested, tliis part is also divided into sections, wliich are as follows: 

1. The economic principles involved. 

2. Interpretation of parasite statistics. 

3. Interpretation of the biological complex. 

4. ITow to profit by existing concUtions. 

5. How to plan for the greatest possible control. 

6. Propagation and artificial introductions. 

7. Objectionable practices. 

8. The economic significance of the investigation. 

1. THE ECONOMIC PRINCIPLES INVOLVED. 

The attempt at utilization of insect enemies in economic ento- 
mology is now receiving so mucli attention that the authors mil 
set down the principles which appear to have been the foundation of 
the work they have done. 

1. Insects in a state of nature are more or less completely held in 
check by natural agencies, in wliich other insects frequently figure 
as of direct or indirect importance. Many insects are controlled 
almost entireh- b}" their insect enemies. No insect is without its 
natural checks. 

2. The relationsliips between an insect and its enemies can not 
be expressed by a simple ratio, nor are they in any way invariable. 
The agencies operating for and against the welfare of a given species 
are so many and of such inconstant magnitude, due to the activities 



84 INSECT ENEMIES OF THE BOLL WEEVIL. 

of otlior agencies, that the effects of one or two agencies of control 
with known strength can not be estimated, because of the many 
other agencies eith(T unknown or of unknown strengtli. 

3. Wlien an injurious insect escapes from its natural surroundings 
to a region where concUtions are favorable for enormous reproduction, 
it may become a pest, but it is never absolutel}" free of natural checks. 
Anthonomus grand/is has never been free of its checks although it 
escaped those of its native home. These agencies of insect control 
are inherent to all countriesr An insect parasite is as hkely to escape 
its original surrouncUngs as a phytophagous insect. 

4. TMien an insect fuids in its vicinity a variety of food closely 
related to its native liost, and that food is more succulent or more 
abundant, there is a possibility that sooner or later the more inviting 
food will become the normal food. Tliis possibility becomes stronger 
when the original food supply fails, if the species is to be continued. 
Not only phytophagous but entomophagous insects have frequently 
been proven to have thus changed their food habits — whether from 
preference or necessity it is nOt known. Leptinotarsa decemlineata 
(the Colorado potato beetle) is an excellent example of this change of 
habit among phytophagous insects. All of the boll-weevil parasites 
are examples of parasites wliich have adjusted their habits in the 
presence of their original hosts. 

5. A crisis in the liistory of a species occurs whenever the food 
su})ply fails. The species may either disperse in search of food, as 
the boll weevil does each autumn, or it may hibernate or sestivate, 
or it may select a new host, or the species may perish. All these 
results occur in nature. All of these alternatives may be chosen by 
different individuals of the same species. It is safe to assume that 
when a species is found to have many hosts that it has undergone 
many crises and that the resultant species is a liighly developed and 
adaptable form. A species most limited in food habit is most liable 
to restriction or extinction and consequently of a lower type than 
one able to meet any emergency. 

6. Wlien a desirable parasite species is known to be adaptable to 
various hosts, a crisis may be artificially superinduced by the timely 
elimination of the favorite hosts, thus forcing the species to attack 
the most predominant near-by related host in the vicinity, or it may 
be taken to an entirely remote or foreign locality and placed near a 
field containing many insects closely related to its original host, 
which it may learn to thrive upon. 

7. The species most available for utilization are those most adapt- 
able to changing en^nronments, or those having the most hosts in 
the given locahty. These other hosts will serve as nurseries for 
parasites. 



INTEEPRETATTOX OF PARASITE STATISTICS. 85 

8. Certain parasites with more or less established habits require 
that their hosts be in certain habitual locations (for exam})le, Neocato- 
laccus requires stem-dwelling hosts), and in like manner there are 
conditions which can be made more favorable for parasite attack 
through cultivation or through plant selection. Furthermore, since 
parasites require different conditions, it is desirable to alter the 
existing conditions so as to make them favorable for as man}^ species 
as possible. In the case of insects extending their range over many 
different climates it should be the aim to introduce parasites best 
adapted to the prevalent conditions. 

2. INTERPRETATION OF PARASITE STATISTICS. 

From the great mass of parasite statistics given in Part I a number 
of important facts need to be considered. 

Parasitic and predatory attack is strongest from August luitil frost 
time. Hence it may be presumed that whatever artificial propaga- 
tion is to be done will be most profitable when conducted during this 
period, provided it does not interfere with early fall destruction of 
stalks, the fundamental cultural remedy against the boll weevil. 

The greatest control of the boll weevil by insects and also by 
all agencies is in hanging squares. As has been stated in Part I 
(sec. 3), the hanging squares are a result of a diagonal absciss layer, 
which causes the drying square to fail in separating itself completely 
from the plant. These squares die on the plant and afl'ord a very 
favorable position for parasitic attacks upon the weevils within. 
The statistics show that insect control in fallen squares is greatest in 
the moist States of Louisiana and Mississippi. This is undoubtedly 
due to some of the new parasites which are accustomed to attacking 
woodland weevils and other insects characteristic of this humid 
region. The insect control in hanging squares is the greatest in the 
comparatively dry States of Texas and Oklahoma. These dry States 
also have a higher combined natural control in the fallen squares 
than in the hanging squares, largely because the climatic conditions 
cause a higher mortality of weevil stages in squares lying on the 
heated surface of the ground. On the contrary, the lumiid States 
have a higher mortality from both climatic and insect agencies m 
hanging squares than in fallen. Furthermore, it has been proven, in 
Part I (sec. 4), that an increase in the amount of hanging squares 
will mcrease the total control. Having these facts in mind, the 
obvious conclusion is that it will be desirable to have varieties of 
cotton which have this tendency best developed. Among the varie- 
ties wliich are now known to retain their squares are the cluster 
varieties, including the Rublee. 



86 INSECT ENEMIES OF THE BOLL WEEVIL. 

The figures show that parasitism becomes very high under favor- 
able conditions and also that agriculture modifies the insect control. 
Obviously therefore those agricultural methods which will favor the 
lughest insect control must be sought. These methods, as now 
known, will be dealt with more fully in a followuig section. 

It was feared for a long time that the parasites of the weevil would 
be held in control by the warm climatic conditions wliich afl'ect the 
boll weevil. This is not so. We have found abundant proofs of the 
fact that a temperature which will kill the boll- weevil larva will not 
kill the egg or small parasite larva in the same cell, and that the 
parasites can develop to maturity on the dried remains of the weevil. 
The temperature fatal to the boll weevil is 123° F., a temperature 
frequently reached on a hot burning soil. We have found in several 
years that a low temperature which will Idll the boll-weevil larva is 
also not fatal to the parasites, for in November, 1907, when 97 per 
cent of all the boll-weevil stages were frozen, no evidence whatever 
could be found of mortality among the parasites. The minimum 
fatal temperature of the boll weevil is 12° F. 

3. INTERPRETATION OF THE BIOLOGICAL COMPLEX. 

The complicated biological factors which have been noted in Part II 
have been summarized briefly in section 16 of that part (p. 82). 
The interpretation of these facts has been suggested in a number of 
places throughout the second part. Hence only a few words are 
necessary at this point. 

The fact that surrounding each cotton field there are numerous 
plants harboring weevils and their parasites is of extreme importance 
in this problem. These parasites are generally capable of attacldng 
the boll weevil under conditions of necessity or alternative choice. 
The aim is therefore to fuid all the methods by which these parasites 
may be forced to leave their native hosts and attack the boll weevil. 
In fact, the entire second part has been devoted to giving these facts 
in order to bring out tliis single point. 

4. now TO PROFIT BY EXISTING CONDITIONS. 

COLLECTION OF COTTON SQUARES IN SCREENED CAGES. 

As has just been pointed out, there are conditions around the cotton 
fields which are potential of a considerable increase in the parasitic 
control of the boll weevil. Probably no other method will yield 
better results than the gathering of the cotton squares which are 
infested and placing them in wire-screen cages of 16 or 18 mesh to 
the inch and placing these cages in selected parts of the cotton 
fields. This method is not new in entomological practice. It has 



HOW TO PROFIT BY EXISTING CONDITIONS. 87 

been used with great value in the freeing of apple orchards in Europe 
from the apple-bud weevil {Antlionomus poinormn). The boll weevils 
can not pass through a 16-mesli or 18-mesh wire screen, while the 
parasites can do so, and therefore the release of these enemies will 
be constantly increasmg the proportion of parasites against the 
weevils. Even if a 14-mesh wire screen is used, only a small pro- 
portion of the weevils can escape tlu-ough it and some gain is effected 
by the release of tlie parasites. In order to demonstrate numerically 
just how this would happen, three hypotheses are presented. In the 
fii'st case squares are collected and put in a 16-mesh wire cage, and 
in the second case squares are collected and put in a 14-mesh wire 
cage, and in the third case no squares are collected. The average per- 
centage of control which follows as a result easily demonstrates the 
advantage which will be almost immediately gained. 

It has been contended and proven that many weevils escai)e 
through the ordinary wire screen. 

/. — Given 10,000 developing stages in a 1-acre field. 

(A) Collect squares containing 50 per cent of the stages and place in l()-mesh 

screened cage 5, 000 

Normal parasitism is 5 per cent 250 

Ants and heat kill 40 per cent 2, 000 

Mortality 2, 250 

Breed 2,750 

There escape through 16-mesh screen — 

10 per cent weevils 275 

90 jjer cent j^arasites 225 

(B) There remain in the field squares containing 50 per cent 5, 000 

Normal mortality as above, 45 per cent 2, 250 

Breed 2, 750 

Some weevils escaped from cages 275 

Total weevils at end of generation 3, 025 

Parasites reared 250 

Parasites escaped from cages 225 

Parasites present in field 475 

There is 1 parasite to every 6.3 weevils. 

II. — Given conditions as above, squares in 14-mcsh screened cage. 

(A) From collected squares breed 2, 750 

There escape through 14-mesh screen — 

40 per cent weevils 1, 100 

All parasites 250 

(B) Breed in field 2,750 

Escaped from cages 1, 100 

Total weevils at end of generation 3, 850 



88 



INSECT ENEMIES OP THE BOLL WEEVIL. 



Parasites reared 250 

Parasitea escaped 250 

Parasites in field 500 

Tliere is 1 parasite to every 7.7 weevilts. 

III. — Given 10,000 developing stages in a 1 -acre field. 

No squares are collected 10, 000 

Normal parasitism, 5 per cent 500 

Ants and heat kill 40 per cent 4, 000 

Mortality 4, 500 

Breed 5,500 

Parasites reared, 500. 

There is 1 j^arasite to every 11 weevils. 

SUMMARY. 



Weevils remain 

Parasites remain 

Ratio of parasites to \vee^•ils 



Squares not 
collected. 



5,500 

500 

1: 11 



Squares collected and 
placed in— 



14-mesh 
wire cage. 



3,850 

500 

1:7.7 



IG-mesh 
wire cage. 



3,025 

475 
1:G.3 



ELIMINATION OF COHOSTS. 



Another practice of undoubted value in bringing about a higher 
percentage of parasitism upon the boll weevil is the eUmination of 
the cohosts of the boll-weevil parasites at proper times. To show 
what has been done in tliis Une, the case of the Dallas farm in 1907 
may be cited. On July 19 of that year a very large hedge of weeds, 
Amhrosia trifida, infested by Lixus scrohicollis was cut. These weeds 
were along the fence adjoining a part of the cotton field which had 
been under close observation for parasites throughout 1906 and the 
spring of 1907. In 1906 there was not found in any plat on tliis 
farm a liigher parasitism than 2 per cent by Eurytoma tylodermatis in 
hanging squares. Eurytoma was very numerous in the Ambrosia 
weeds next to tliis field, but did not appear to attack the weevil in 
large numbers. Before the weeds were cut in 1907 the two plats 
nearest these weeds averaged 26.76 per cent and 16.79 per cent 
parasitism by Eurytoma. On August 17, about a month after these 
weeds were cut, the two plats just mentioned had, respectively, 37.50 
per cent and 26.66 per cent parasitism by Eurytoma. This striking 
gain adjoining the w^eeds was not reflected by j)arts of the field farther 
removed. 



HOW TO PROFIT BY EXISTTXG CONDITIONS. 89 

EARLY DESTRUCTION OF THE COTTON STALKS. 

Tliero can be little doubt that the early destruction of the cotton 
stalks, in addition to depriving the boll weevil of its food plant, will 
also cause the parasites to seek a series of hosts which can carry them 
through the winter period. In order to prove that fall destruction 
does not have an injurious effect upon parasite control, we would cite 
the discussion of the Victoria fields, in which various methods of fall 
destruction were carried out, as discussed in Part I, section 6. As a 
further proof the famous 01i\'ia fall-tlestruction experiments may be 
considered. 

On October 1 to 10, 1906, all of the cotton plants in over 400 acres, 
constituting the entire OUvia cotton community in Calhoun County, 
Tex., were cut and burned under the direction of Mr. J. D. Mitchell. 
Accoiding to the rearing records in our possession, the parasites 
developing in this cotton would all be mature before November 10, 
and if they hibernated, would have to do so as adults. No other 
cotton existed within 12 miles, as the community is completely iso- 
lated by water and marshland. 

Cotton was planted about March 15, 1907. On April 15 no boll- 
v>^eevil work could 1)0 found, Init on May 7 a single weevil was found 
after a careful examination of eight fields. On the same date at Six 
Mile settlement, across the bay near Port Lavaca, there was consider- 
able infestation. If the parasites hibernated as adults they would be 
dead long before the middle of June. If they could have hibernated 
as immature stages they would have matured l>y ]\Iarch 15, and under 
normal conditions three generations would have passed by June 15. 
The infestation was still very shght in July. It must be argued, 
therefore, that any boll-weevil parasites must l)e breeding on some 
other weevil, if they did not perish. 

On August 22, 1907, Mr. Mitchell found parasites with weevil- 
infested squares on a field in the opposite part of the community to 
that in which he first found the weevil infestation. The obvious 
inference is that a rotation of hosts occurred during the i)eriod of the 
boll weevil's absence. 

Having planned the cropping system, it is also best to prepare the 
fields early for cotton and plant as early as possible. Of course, most 
of the reasons for earl}^ planting of cotton are well known and the 
practice is very common, but in this connection it must be said that 
such early planting has the actual advantage of enabhng the para- 
sites to start early. 

Care must be given to the choice of tlie cotton variety which is to 
be used. Frequent recommendations have been made of varieties 
with hglit foliage, early maturing fruit, short nodes, and determinate 
growth. All of these qualities are favorable to parasite control, 



90 INSECT ENEMIES OF THE BOLL WEEVIL. 

especially since such plants afford much more sunlight on the ground. 
The ants and also the parasites prefer much more to attack the 
squares which are dried out than moist squares. It seems that they 
can more readily penetrate the hnings of the square. In addition to 
these qualities of the cotton variety, the use of a variety with at 
least a moderate amount of nectar is also advised. The reason for 
tliis has been explained in preceding jiaragraphs. Finally, the tend- 
ency of plants to retain the squares must be again mentioned. If a 
variety can furnish the desired quahties of early producing, produc- 
tiveness, and quahty of hnt, as well as a diagonal absciss layer on the 
square, that variety should be chosen above others. 

If at all possible, it is advisable to plant the rows far apart or on 
the check-row system, in order to give the necessary amount of sun- 
Hght. The cultivations to follow tliis should be with the purpose 
of obtaining a dust mulch, for with such a mulch the surface of the 
soil may be heated to a much higher degree than by deep and lumpy 
cultivation, and the control of the l:)oll weevil will thus be greatly 
increased, through the drying effect upon fallen squares. 

5. now TO PLAN FOR THE GREATEST POSSIBLE CONTROL. 

As it has been proven that many agricultural processes are favor- 
able to the development and attack of parasites and enemies, there 
can be no question but that it is desirable to plan to obtain the great- 
est amount of this beneficial aid. 

There are a few plants which have no objectionable quahties in 
themselves which might with good reason be planted adjacent to the 
cotton fields in order to induce the attack of weevils which act as 
hosts of the boll-weevil parasites. For instance, the presence of a 
hedge of blackberries or dewberries along the fence means the pre- 
sence of Antlionomus signatus, the blackberry bud weevil, with its 
numerous parasites, all of wliicli attack the boll weevil. The para- 
sites would be able to carry on a generation in the spring before the 
boll weevils were breeding and would mature in plenty of time to 
attack the first developing stages of the boll weevils. 

It would seem advisable to plant a hedge of the flowering shrub 
Amorpha fruticosa, which is the host plant of Laria exigua. This 
Httle wevil is very abundantly parasitized. 

In planning the cropping sj^-stem there can be no possible harm 
in arranging to have a forage or hay crop adjacent to the cotton 
field. In case a forage crop is used, cowpeas with the ever-present 
cowpea pod weevil would undoubtedly bring about the presence 
of several important parasites. The early removal of the cowpeas 
for fodder would force the parasites to attack the boll weevil. In 
the case of a hay field, the process of haying and subsequent curing 



PROPAGATION AND AETIFICIAL INTKODUCTIONS. 91 

would enable the parasites present in the various weeds to escape 
and attack the most abundant host, namely, the boll weevil. 

If, with all these precautions, the boll weevils are very numerous 
in the field, and the expense is not too great, much can bo gained by 
picking the squares and placing them in cages, as has been described 
in a previous section. 

Finally, at the proper season for haying, the actual methods of 
cutting and preparing the hay will without doubt furnish still greater 
control to the weevil. Some time in Sei)tember, if not before, whether 
haying is carried on or not, there should be a thorough cutting of all 
weeds around the cotton field in order to force the parasites to the 
boll weevil and also to get rid of favorable hibernation quarters for 
the boll weevil. 

6. PROPAGATION AND ARTIFICIAL INTRODUCTIONS. 

The propagation of parasites under artificial conditions and their 
introduction are attended with a great amount of labor and expense 
and have mau}^ technical difficulties. The simplest form of propaga- 
tion is the collection of infested squares at one locality and the ship- 
ment of them to another locality, where they are placed in the field 
to await results. There are good reasons for attempting thus to 
introduce parasites. It has been found by very close observations 
that the parasites are not evenly distributed, but that each species 
has a more or less defimtely defined geographical region. This is 
no doubt due to the distribution of the normal host weevils. The 
purposes of introduction are to take these parasites from their native 
localities and place them in geographical regions in which they do 
not at present exist. Definite proofs that results can be obtained 
in this manner were to be had at Dallas on tlie experimental farm in 
1906 and also in 1907. The 1906 experiment has been fully described 
in the first report on the parasites of the boll weevil (Pierce, 1908a). 
In 1907 a similar experiment was tried l^y the release of large numbers 
of adult parasites. These parasites were carried to a field in small 
screen cages containing foliage, so that the parasites might not become 
overheated. The cages were opened in the shade, and the parasites 
allowed to fly out in any direction which they pleased. While many 
species of parasites were released in this manner, they did not all 
show the results that were expected, but the release of Catolaccus 
incertus in a given part of the field accomplished an increase in the 
control in hanging squares by this species. In two other parts of the 
field Microhracon meUitor was released, and it also showed good gains. 
As Microhracon was released on this farm both in 1906 and 1907, it may 
be useful to compare the percentages of parasitism at various periods. 
In August, 1906, this species furnished 8.5 per cent parasitism in hang- 



92 



INSECT ENEMIES OF THE BOLL WEEVIL. 



ing squares; in September, 1906, this had risen to 10.2 per cent; in 
July, 1907, the parasitism by this species was 35.2 per cent, and in 
August, 1907, it had risen to 39.8 per cent. 

At Shreveport, La., in 1908, many specimens of Catolaccus incertus 
and Microbracon mellitor were released. Table XXII gives an idea of 
the results and shows the expected increase by Catolaccus in both 
hanging and fallen squares and by Microbracon in hanging squares. 

Table XXII. — Experiment in artificial introduction of Catoloccus incertiis and 
Microbracon mellitor, Shreveport, La., 1908. 





Plat. 


Date. 


Percentage of mortality. 


Gain in mortality. 


Class of forms. 


Total. 


Para- 
sites. 


Cato- 
laccus. 


Micro- 
bracon. 


Total 
para- 
sites. 


Cato- 
laccus. 


Micro- 
bracon. 


Fallen squares 


Release. .. 
. do 


Oct. 5 
Oct. 28 
Oct. .5 
Oct. 28 
Oct. 6 
Oct. 2(1 


30.44 
37. 90 
40. 00 
42. 33 
47.15 
04.80 


5.93 

15.74 
10.50 
10. 00 
9. 90 
37.84 


4.23 
10.80 
5.55 
8.00 
4.39 
10.81 


1.70 
2.10 
3.70 
5.00 
3.29 
18. 91 


Per cent. 


Per cent. 


Per cent. 


Do . . 


105 


1.50 


33 


Do 


Check 

...do 




Do 


52 


44 


35 


Hanging squares... 


lielease. . . 
...do 




Do 


282 


148 


477 



RELEASE CAGES. 

In order to obtain satisfactory results from the release of infested 
material, it is necessary to place the material in cages from which 
the injurious weevils can not escape but which will still allow the 
parasites egress. This principle has been exi)lained in other sections. 
There is also another important consideration in the construction of 
the cages. When a large amount of material such as this is collected 
in a small space it furnishes great inducements to attack by colonies 
of ants. The only way that the material can be protected from total 
destruction by ants is the isolation of the cage on legs by the use of 
" inverted cups " containing oil, or by greasing the legs in some 
manner. 

TRANSFER OF ANT COLONIES. 

Since the work of ants is always very favorable to control, means 
should be devised of increasing their numbers in the cotton field. 
The dust-mulch method of cultivation is very favorable to the ants 
in that it does not disturb their colonies after they have commenced 
breeding. This is a very im})ortant matter to consider. The late 
Mr. F. C. Pratt, in working with the horn fly {Lyperosia irritans 
L.) discovered that fresh manure containing numerous fly larvae 
is very attractive to Solenopsis, and tliat these ants seem to trans- 
fer their whole colony at times to the manure. Mr. Wilmon Newell, 
in connection with the Argentine ant investigations, at a later 
date, found that he could trap immense colonies of the Argentine 



OBJECTIONABLE PRACTICES. 93 

ant {Iridomyrmex Jiumilis) by means of boxes containing manure. 
These observations are very suggestive, for they point out the possi- 
bihty that colonies of ants can be obtained by placing fresh manure 
in boxes near ant colonies. When sufficient numbers have entered, 
they may be boxed up for removal to a place desired. In tliis manner 
great colonics could be transferred bodily for considerable distances. 

7. OBJECTIONABLE PRACTICES. 

There are several practices which are quite objectionable from the 
standpoint of encouraging the ])arasites and most of which have 
also been found objectionable from purely cultural standpoints. 
Wlien the cotton is planted closelv on moist soil its growth is mainly 
vegetative and consequently immense stalks may have very little 
fruit. Agriculturists have alwa3^s pointed out that large cotton 
plants need plenty of room in order to produce fruit. Field examina- 
tions to determins the mortality of the boll weevil from various causes 
have always shown that the parasitism is greatest in the portions of a 
field where tlie foliage is lightest. A notable example was found at 
Natchez, Miss., where in a single field the growth was very irregular. 
One spot seems to have been used for feeding cattle and was very 
fertile. On this spot the cotton grew 6 or 8 feet tall and the ground 
was densely shaded. Here the mortality of the weevil was very low, 
and there was scarcely any control by insects. One hundred feet 
from this was a thin piece of ground where the cotton plants were 
barely 2 feet high, but they were loaded with bolls and showed a 
much higher percentage of mortality, especially by insect enemies. 
An actual count of the number of bolls in the two parts of the field was 
greatly in favor of the smaller plants. 

Late planting has been proven objectionable from almost every 
stand])oint from which it has been viewed. Under existing circum- 
stances there are no valid arguments for late planting. From the 
standpoint of control by parasites late planting simply delays the 
attack of parasitic enemies and reduces the amount of control in the 
fall at a critical time. 

It is believed that the use of varieties which always tend to drop 
their squares is objectionable if varieties with the opposite tendency 
can be found with the same qualities of production. 

The iwactice of 'picking squares and then burning them can not he 
condemned too stronghj. The i)lanters are by this practice almost 
nullifying the good work that they do by picking the squares. They 
are doing nothing more or less than destroying their best friends 
when they burn these squares. This may be proven by an hypothesis 
similar to those presented (p. S7) in demonstrating the value of collect- 
ing the infested squares. 



94 INSECT ENEMIES OF THE BOLL WEEVIL. 

Given 10,000 developing stages of the boll weevil in a 1 -acre field. 

(A) Collect and burn squares containing 50 per cent of the stages 5, 000 

This destroys all parasites as well as weevils. 

(B) There remain in the field squares containing 50 per cent of the stages 

present 5, 000 

Normal parasitism 5 per cent 250 

Ants and heat kill 40 per cent 2, 000 

Mortality 2, 250 

Weevils to breed 2, 750 

Parasites present in field, 250. 

There is 1 parasite to every 11 weevils. 

Tliis method undoubtedly greatly reduces the total number of 
weevils in the field, but, as can be readily seen, the proportion of 
parasites to weevils is the same as if nothing had been done — namely, 
1 to 11. It was shown that by placing the squares in 16-mesh wire 
cages the proportion would be 1 to 6.3. Hence it appears that by the 
caging method the planter leaves in his field a more active agency 
than he had before to attack the many weevil stages he has undoubt- 
edly missed, whereas by the burning method he has not in the least 
improved his field conditions. 

8. THE ECONOMIC SIGNIFICANCE OF THE INVESTIGATION. 

In final summary the following points are emphasized: 

I. The control of the holl weevil hy insect enemies is sufficiently great 
to give it a liigh rank in the struggle against the pest. A considerable 
portion of the insect control would not he accomplished hy any other 
factor; hence it is hy no means to he neglected. 

The number of species of insects attacking the developing stages 
is 49. 

The control in any given place consists of the combined work of 
several different species. 

Places having the largest number of controlling insects have the 
highest percentage of control. 

In many places insect control is considerably greater than climatic 
control or than any other class of factors. 

The average insect control is 20 per cent of all immature stages or 
two-fifths of the entire natural control. 

The cotton leaf-worm is a valuable enemy of the boll weevil when 
it defoliates the cotton after September 1, a date beyond which new 
squares can not be expected to mature. It kills many weevils by 
starvation, kills many others while consuming the squares, and 
finally forces a premature hibernation which is generally fatal. 



ECONOMIC SIGNIFICANCE OF INVESTIGATION. 95 

II. The amount of control due to the various factors at work in any 
given place should he increased if possible. Parasites can he introduced 
into new fields. 

In order to prevent serious injury to cotton, the mortality of the 
weevil should be above 90 per cent. It has averaged over 57 per cent 
for four years and has reached almost 100 per cent several times. 

"VVliile climatic influences occasionally bring the control above 90 
per cent, they can not be regulated or in any way directly utilized. 

Although the insect enemies present at a given place may be 
accomplishing the greatest amount of work possible, the fact remains 
that if other species of enemies are introduced and become estab- 
lished the control can be increased. 

Since certain parasites attack the weevil preferably in dry locations 
and others in wet locations, and since some prefer to attack the 
infested forms on the plant, while others seek them on the ground, 
it is possible to select the insect agencies so as to obtain the least 
amount of lost or duplicated energy. 

III. The parasites and predators which attack the holl weevil are 
native insects, already present in a given territory he fore the weevil 
arrives. 

The predators, especially ants, will attack almost any kind of 
insect food. The parasites in nearly all cases are capable of attack- 
ing almost any kind of weevil breeding in herbs above ground or in 
fruits. 

The parasites have proven their ability to adjust themselves to 
the boll weevil by attacking it in its first generation in newly infested 
territory in instances where the actual sources of the parasites were 
demonstrable. 

The weeds surrounding the cotton fields contain many weevils 
which are harboring multitudes of available parasites. These para- 
sites may be induced to attack the boll weevil by the timely elimina- 
tion of their native hosts. 

This leads to the recommendation that planters cut the iveeds adjoin- 
ing the cotton fields, along the roadsides, turn rows, and fences ahout the 
time of the maturing of the crop. 

It also leads to the recommendation that a field adjoining the cotton 
he used as a pasture or hay field, and that this fi.eld he mowed early in 
the fall. The usual haying will also bring about the same result- 
namely, the elimination of other plants harboring weevils which 
attract the parasites needed in the cotton patch. 

It is advisable to have in the vicinity of the cotton field such plants 
as the dewberry, Croton, Amorpha, cowpeas, etc., which contain other 
hosts of the boll-weevil parasites. 



96 INSECT ENEMIES OE THE BOLL WEEVIL. 

IV. The cultural methods of controlling the cotton hall weevil are the 
most favorable methods of cotton culture from the parasitic standpoint. 

The tendency of the principal boll-weevil parasites to prefer light 
and heat leads immediately to a long series of recommendations. 

Heat on the ground is essential for the climatic control of the 
weevil and also for parasitic control. Although the two factors 
overlap, each accomplishes considerable independent control. 

A heated condition of the ground may he accomplished hy planting 
the rows far apart, hy check-row planting, hy flat cultivation, or hy 
planting varieties which have short Umhs, or shed their foliage early, or 
have small leaves. 

Fall destruction of the cotton plants cuts off the parasites from 
breeding on the weevil but sends them to other hosts upon which 
tliey can breed a winter generation, or pass hibernation, thus gaining 
not only a generation on the weevil but providing for themselves 
during the winter. 

The early planting of cotton in the spring makes it possible for the 
earliest parasites to attack the weevil. 

V. The tendency to retain infested fruit, whicli is displayed by 
certain varieties, is worth consideration. 

The fact that many more parasites are reared in hanging squares than 
in fallen squares malies it desirahle in humid regions to have many of 
the hanging squares in afield in order to serve as a nursery of parasites 
for the iveevils in the fallen squares. 

Varieties which show an elongate diagonal connection between 
the scpiare and stem will tend to have an imperfect absciss layer 
formed. Prominent in this class are the cluster boll varieties of 
cotton. It is recommended that search he made for such a variety as 
will retain its infested forms and at the same time fulfill the other require- 
inents in the making of a good crop. 

VI. Any step which will diminish the number of weevils and not 
diminish the number of parasites in a held will of course increase the 
percentage of parasites present. 

The most important step of this kind is the collection of infested squares 
and placing them in cages loith a screen through which the weevils can not 
escape hut the parasites can. 

Ant colonies may be introduced into the fields in boxes of fresh 
manure. 

If squares are collected, they should not he hurned, hut should he placed 
in screened cages. 



INSECT ENEMIES OF THE BOLL WEEVIL. 97 

BIBLIOGRAPHY. 

Aldrich, John Merton. 

1905. Catalogue of North American Diptera. <Smithsonian Misc. Coll., vol. 46, 
no. 1444, pp. 426, 427. 
AsHMEAD, William Harris. 

1896. Descriptiona of new parasitic Hymenoptera, II. <Trans. Amer. Ent. 

Soc, vol. 23, pp. 218-219. 
1902a. A new Bruchophagus from Mexico. <Boletin de la Comision de Para- 
sitologia, vol. 1, no. 9, pp. 404. (Kor Spanish translation see Herrera.) 
Banks, Nathan. 

1904. A treatise on the Acarina or mites. <Proc. U. S. Nat. Mus., vol. 28, no. 

1382, pp. 74-76. 
190C. A revision of the Tyroglyphidse of the United States. <U. S. Dept. Agr., 
Bur. Ent., Tech. Ser. 13, p. 17, PI. IV. 
Barreda, L. de la. 

1904. El picudo del algodon. Salvacion de la riqueza de la frontera. <Comi8ion 

de Parasitologia Agricola, Cir. 6, pp. 14-27. 
Chittenden, Frank Hurlbut. 

1893«. The strawberry weevil. <U. S. Dept. Agr., Div. Ent., Ins. Life, vol. 5, 

pp. 181-182. 
18936. Observations on some hymenopterous parasites of Coleoptera. <U. S. 

Dept. Agr., Div. Ent., Ins. Life, vol. 5, p. 250. 
1895. The potato-bud weevil (AntJionoinus nigrinus Boh.). <U. S. Dept. Agi-., 

Div. Ent., Ins. Life, vol. 7, pp. 351-352. 

1897. The strawberry weevil {Anthonomus signatus Say). <LT. S. Dept. Agr., 

Div. Ent., Cir. 21, p. 4. 
1899. Insects injurious to beans and peas. <U. S. Dept. Agr., Yearbook, 1898, 

pp. 242, 245. 
1902. The potato stalk weevil. <U. S. Dept. Agr., Div. Ent., Bui. 33, n.s., p. 17, 
1908. An injurious North American species of Apion, with notes on related 

forms. <U. S. Dept. Agr., Bur. Ent., Bui. 64, Pt. IV, pp. 30-32. 
Cook, Orator Fuller. 

1904a. An ant enemy of the cotton boll weevil. -^U. S. Dept. Agr., report 78, pp.7, 

May 27. 
19046. Report on the habits of the kelep, or Guatemalan cotton-boll weevil ant. 

<U. S. Dept. Agr., Bur. Ent., Bui. 49, 15 pp., August. 

1905. The social organization and breeding habits of the cotton-protecting kelep 

of Guatemala. <U. S. Dept. Agr., Bur. Ent., Tech. Ser. 10, pp. 55. 

COQUILLETT, DaNIEL WiLLIAM. 

1897. Revision of the Tachinidae of America north of Mexico, a family of para- 
sitic two-winged insects. <U. S. Dept. Agr., Div. Ent., Tech. Ser. 7, 
pp. 50, 51. 
Crawford, James Chamberlain. 

1907a. New hymenopterous parasites of Anthonomus grandh Boh. <^Can. Ent., 
vol. 39, pp. 133, 134, April. 

19076. New North American Hymenoptera. <Journ. N. Y. Ent. Soc, vol. 15, 
no. 4, p. 179, December. 

1908. Some new Chalcidoidea. <Proc. Ent. Soc. Wash., vol. 9, pp. 157-160, 
April 6. 

1909a. New Chalcidoidea. <Proc. Ent. Soc. Wash., vol. 11, p. 52. 

19096. Two new species of the genus Tetraetichue. <Proc. Ent. Soc. Wash., vol. 
11, p. 150, October 5. 
16844°— Bull. 100—12 7 



98 INSECT ENEMIES OF THE BOLL. WEEVIL. 

Foster, F. 

1908. The iutroduction of Iridomynnex humilis (Mayr) into New Orleans. 

<Journ. Econ. Ent., vol. 1, no. 5, pp. 289-293, October 5. 

GiRAULT, A. ArSENE. 

1907. The lesser peach borer. <U. S. Dept. Agr., Bur. Ent., Bui. 68, Pt. IV, 
p. 45. 

Contains an undoubtedly erroneous reference to (Bracon) 3IicrohraconmeUiior Say . 

Herrera, Alfonso L. 

1902a. Sexto informe acerca del picudo del Algodon {Insanthonomus grandis 
I. C. Cu.): Pequena avispa pardsita del picudo. <Boletin de la 
Comision de Parasitologia Agricola, vol. 1, no. 9, pp. 403-404. 
This is a translation of Ashrnead 1902b. 
19026. Ilormiga deatructora del picudo. <Loc. cit., pp. 404-406. 
Tliis contains a translation of Wheeler, 1902. 

Hinds, Warren Elmer. 

1907rt. An ant enemy of the cotton boll weevil. <U. S. Dept. Agr., Bur. Ent., 

Bui. 63, Pt. Ill, pp. 45-48, February 5. 
19076. Some factors in the natural control of the Mexican cotton boll weevil. 

<U. S. Dept. Agr., Bur. Ent., Bui. 74, December 14. 

Hood, Clarence Ellsworth. 

1909. Types of cages found useful in parasite work. <Journ. Econ. Ent., vol. 2, 

no. 2, pp. 121-124, April 15. 

Howard, Leland Ossian. 

1897. The Mexican cotton boll weevil (Anthonomus grandis Boheman). <U. S. 
Dept. Agr., Div. Ent., Cir. 18. 

Hunter, Walter David. 

1907. Some recent studies of the Mexican cotton boll weevil. <Yearbook 
U. S. Dept. Agr., 1906, pp. 318-322. 

Hunter, Walter David, and Warren Elmer Hinds. 

1904. The Mexican cotton boll weevil. <U. S. Dept. Agr., Div. Ent., Bui. 45, 

pp. 104-110. 

List of parasites and predators; adds as new records Sigalphus curculionis Fitch, Cato- 
ItKcus incertus Ashmead, Urosigalphus (robuslus Ashmead), Bracon {dorsator Say), and 
Eurytoma tylodermatis Ashmead, as well as an entomopliasous fungus, Aspergillus sp. 

1905. The Mexican cotton boll weevil. <U. S. Dept. Agr., Bur. Ent., Bui. 51, 

pp. 143-150. 

Hunter, Walter David, Wilmon Newell, and William Dwight Pierce. 

1907. The insect enemies of the boll weevil. <T.oui8iai]a Crop Pest Comm., 
Cir. 20, December. 

Mally, Frederick William. 

1902. Report on the boll weevil. <Public Printer, Austiii, Tex., pp. 23-24. 

Ilecords (Bracon) Microbracon mellitor Say, Ccrambycobius cyaniceps Ashmead, and 
Eurytoma .sp. from the boll weevil. 

Morgan, Alfred Cookman. 

1907. A predatory bug reported as an enemy of the cotton boll weevil. <U. S. 

Dept. Agr., Bur. Ent., Bui. 63, Pt. IV, pp. 49-54, February 8. 

Newell, Wilmon, and R. C. Trehearne. 

1908. A new predaceous enemy of the cotton boll weevil. <Journ. Econ. Ent., 

vol. 1, no. 4, p. 244, August 15. 



BIBLIOGRAPHY. 99 

Pierce, William Dwight. 

1907a. Notes on the biology of certain weevils related to the cotton boll weevil. 

<U. S. Dept. Agr., Bur. Ent., Bui. G3, Pt. II, pp. 37-44, Februarys. 
19076. On the biologies of the Rhynchophora of North America. <Ann. Rept. 

Nebraska State Board Agr., 1906-7, pp. 261, 263, 268, 269, 270, 271, 

272, 274, 276, 278, 279, 282, 283, 285, 295, September. 
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pp. 356-363 (October), 379-385 (November). 
1908a. Studies of parasites of the cotton boll weevil. <U. S. Dept. Agr., Bur. 

Ent., Bui. 73, p. 63, January 21. 
19086. The economic bearing of recent studies of the parasites of the cotton boll 

weevil. <Journ. Econ. Ent., vol. 1, no. 2, pp. 117-122, April 15. 
1908c. Factors controlling parasitism with special reference to the cotton boll 

weevil. <Journ. Econ. Ent., vol. 1, no. 5, pp. 315-323, October 15. 
1908c/. A list of parasites known to attack American Rhynchophora. ^Journ. 

Econ. Ent., vol. 1, no. G, pp. 380-396, December 15. 
1910. On some phases of parasitism displayed by insect enemies of weevils. 

<Journ. Econ. Ent., vol. 3, pp. 451-488, December 15. 
Pratt, Frederick Charles. 

1907. Notes on the pepper weevil. <U. S. Dept. Agr., Bur. Ent., Bui. 63, Pt. V, 

p. 56, February 9. 
Rangel, a. F. 

1901a. Segundo informe acerca del picudo del algodon (Insanthonovius grandis 
I. C. Cu.). <Boletin de la Comisi6n de Parasitologia Agricola, vol. 1, 
no. 5, pp. 171-176. 
19016. Tercer informe acerca del picudo del algodon. <Boletin de la Comision 

de Parasitologia Agricola, vol. 1, no. 6, pp. 197-206. 
1901c. Cuarto informe acerca del picudo del algodon {Tnsanthonomus grandis 
I. C. Cu.). <;Boletin de la Comision de Parasitologia Agricola, vol. 1, 
no. 7, pp. 245-261. 
Riley, Charles Valentine, and Lbland Ossian Howard. 

1890. Some of the bred parasitic Hymenoptera in the National Museum collec- 
tion. <U. S. Dept. Agr., Div. Ent., Ins. Life, vol. 2, pp. 348-350, 
353; vol. 4, pp. 122, 123. 
ScHWARz, Eugene Amandus. 

1905. Note on D ory my rm ex pyr amicus Roger. -<Proc. Ent. Soc. Wash., vol. 7, p. 4. 
Townsend, Charles Henry Tyler. 

1895. Reports on the Mexican cotton boll weevil in Texas {Anthonomus grandis 
Boh.). <U. S. Dept. Agr., Div. Ent., Ins. Life, vol. 7, pp. 295-309. 

1908. The taxonomy of the muscoidean flies, including descriptions of new genera 

and species. <Smithsonian Misc. Coll., vol. 51, no. 1803, pp. 56-58, 86. 
Wheeler, W^illiam Morton. 

1902. Formica fusca Linnaeus, subsp. subpolita Mayr., var. perpilosa n. var. 
<;BoIetin de la Comision de Parasitologia Agricola, vol. 1, no. 9, pp. 
406-407. (For Spanish translation see Herrera.) 



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